move symbolizer to json into core
symbolizer json grammar (needs more work)
c++11
fix svg_renderer
avoid dereferencing pointer more than once
Merge branch 'master' of github.com:mapnik/mapnik into expr-v2
generic ```to_integral``` helper function (convert strongly typed enumeration values to underlying type)
convert json value into symbolizer_base::value_type
register target type for symbolizer properties
symbolizers: set_property helper
Merge branch 'expr-v2' of github.com:mapnik/mapnik into expr-v2
avoid signed comparison warning in symbolizer test
Revert "don't set -stdlib in CXXGLAGS"

This reverts commit 62c06eabcc18cfb8a63ee764ccbe4d86bb90eefc.
Merge remote-tracking branch 'upstream/expr-v2' into mla-expr-v2-renderer-common