3.x port of localized font caching and then some
fix benchmark compile
c++ style
unique_ptr for font_face_set
ignore font cache in map assignment and comparison
cleanup
add code comments to create_face
simplify code in create_face
reduce compile time by minimizing template instantiaions
install doc: note minimum harfbuzz version for font-feature-settings - refs #2456
travis: use harfbuzz v0.9.35
Merge pull request #2466 from mapnik/reduce-compile-times

reduce compile time by minimizing template instantiations
Revert "ditch boost/function" - refs #2465

This reverts commit 24052580b951f1d58a5a0edaf81572b3e8267836.
fix compile of (currently unsed) symbolizer_grammar.hpp
break apart symbolizer.hpp + fwd declars + svg output grammar impl
new files
Merge branch 'master' of github.com:mapnik/mapnik into localized-font-cache

Conflicts:
	src/build.py
Merge branch 'master' of github.com:mapnik/mapnik into localized-font-cache
travis: try more aggressive JOBS again - refs #2439
csv plugin: only attempt to parse ascii as numbers - closes #2450