ENH: add alternative STL ASCII parsers

- In addition to the traditional Flex-based parser, added a Ragel-based
  parser and a handwritten one.

  Some representative timings for reading 5874387 points (1958129 tris):

      Flex   Ragel   Manual
      5.2s   4.8s    6.7s         total reading time
      3.8s   3.4s    5.3s         without point merging

src/fileFormats/stl/STLAsciiParseI.H

@@ -0,0 +1,192 @@
+/*--------------------------------*- C++ -*----------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 2018 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+\*---------------------------------------------------------------------------*/
+
+// * * * * * * * * * * * * Protected Member Functions  * * * * * * * * * * * //
+
+inline void Foam::Detail::STLAsciiParse::beginSolid(word solidName)
+{
+    if (solidName.empty())
+    {
+        solidName = "solid";  // Could also use solid0, solid1, ...
+    }
+
+    auto iter = nameLookup_.cfind(solidName);
+    if (iter.found())
+    {
+        if (groupId_ != iter.object())
+        {
+            sorted_ = false;  // Group appeared out of order
+            groupId_ = iter.object();
+        }
+    }
+    else
+    {
+        groupId_ = sizes_.size();
+        if (nameLookup_.insert(solidName, groupId_))
+        {
+            names_.append(solidName);
+            sizes_.append(0);
+        }
+        else
+        {
+            FatalErrorInFunction<< "Duplicate solid-name: " << solidName
+                << exit(FatalError);
+        }
+    }
+}
+
+
+inline void Foam::Detail::STLAsciiParse::beginFacet()
+{
+    nFacetPoints_ = 0;
+    nVertexCmpt_ = 0;
+}
+
+
+inline void Foam::Detail::STLAsciiParse::resetVertex()
+{
+    nVertexCmpt_ = 0;
+}
+
+
+inline bool Foam::Detail::STLAsciiParse::addVertexComponent(float val)
+{
+    currVertex_[nVertexCmpt_] = val;
+
+    if (++nVertexCmpt_ == 3)
+    {
+        points_.append(currVertex_);
+        nVertexCmpt_ = 0;
+        ++nFacetPoints_;
+    }
+
+    return !nVertexCmpt_;
+}
+
+
+inline bool Foam::Detail::STLAsciiParse::addVertexComponent(const char* text)
+{
+    //-> safer, but slower: readFloat(text, currVertex_[nVertexCmpt_]);
+    currVertex_[nVertexCmpt_] = ::atof(text);
+
+    if (++nVertexCmpt_ == 3)
+    {
+        points_.append(currVertex_);
+        nVertexCmpt_ = 0;
+        ++nFacetPoints_;
+    }
+
+    return !nVertexCmpt_;
+}
+
+
+inline void Foam::Detail::STLAsciiParse::endFacet()
+{
+    if (nFacetPoints_ == 3)
+    {
+        facets_.append(groupId_);
+        sizes_[groupId_]++;
+    }
+    else
+    {
+        if (nFacetPoints_ > 3)
+        {
+            nFacetPoints_ -= 3;
+        }
+
+        if (nFacetPoints_)
+        {
+            points_.resize(points_.size() - nFacetPoints_);
+        }
+    }
+
+    nFacetPoints_ = 0;
+}
+
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+inline Foam::Detail::STLAsciiParse::STLAsciiParse(const label approxNpoints)
+:
+    sorted_(true),
+    groupId_(-1),
+    lineNum_(1),
+    nFacetPoints_(0),
+    nVertexCmpt_(0),
+    points_(approxNpoints),
+    facets_(approxNpoints/2)
+{}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+inline void Foam::Detail::STLAsciiParse::clear()
+{
+    sorted_ = true;
+    groupId_ = -1;
+    lineNum_ = 0;
+
+    nFacetPoints_ = 0;
+    nVertexCmpt_ = 0;
+
+    points_.clear();
+    facets_.clear();
+    names_.clear();
+    sizes_.clear();
+    nameLookup_.clear();
+}
+
+
+inline bool Foam::Detail::STLAsciiParse::sorted() const
+{
+    return sorted_;
+}
+
+
+inline Foam::DynamicList<Foam::STLpoint>& Foam::Detail::STLAsciiParse::points()
+{
+    return points_;
+}
+
+
+inline Foam::DynamicList<Foam::label>& Foam::Detail::STLAsciiParse::facets()
+{
+    return facets_;
+}
+
+
+inline Foam::DynamicList<Foam::word>& Foam::Detail::STLAsciiParse::names()
+{
+    return names_;
+}
+
+
+inline Foam::DynamicList<Foam::label>& Foam::Detail::STLAsciiParse::sizes()
+{
+    return sizes_;
+}
+
+
+// ************************************************************************* //