Factored common renderer code from SVG renderer.
use mapnik::value_xxx types
Factored out common code for building symbolizer.

There's a lot of code common between symbolizers which do things
like layout, setup, etc... So it seems sensible to extract the
common operations & loops into a single place which is
independent of the actual renderer.

I've started doing this with C++11 lambdas, although that might
not be the best implementation long term. Should be easy enough
to change, though.
Factored out common implementation of point symbolizer.
Factored out common implementation of raster symbolizer.
avoid duplicate call to start_layer_processing
avoid duplicate call to start_layer_processing

Conflicts:
	include/mapnik/feature_style_processor_impl.hpp
NumericWrapper helper class to pass correct numeric type
value_bool, value_integer, value_double to symbolizer property
(there must be a better way ;)
add extract method to access underlying type from mapnik.Symbolizer
Factored out markers symbolizer logic.

It's not ideal - there's still a bunch of "dispatch" objects from
which the common elements could be factored for greater
readability.
Merge branch 'master' of github.com:mapnik/mapnik into expr-v2

Conflicts:
	src/load_map.cpp
add __hash__ to all symbolizers
add equality comparator ``` .def(self == self) // __eq__```
c++11 style for loop
Factored out common implementation of polygon symbolizer.
c++11 : use ```constexpr name2int`` switch instead of if/else
revive stroke linecap/linejoin
Merge remote-tracking branch 'upstream/expr-v2' into mla-expr-v2-renderer-common
move symbolizer to json into core
symbolizer json grammar (needs more work)
c++11