Parse and support placement of multiple text layouts within a single text symbolizer.
Add python binding for Layout node in format tree.
Tests for multiple text layout placements.
Replace tabs with spaces. Remove unused method prototype.
Merge branch 'expr-v2' of github.com:mapnik/mapnik into jmh-text-layouts

Conflicts:
	tests/visual_tests/test.py
Update test cases.
Use make_shared to create shared_ptr.
Create tests for line-symbolizer, using expressions for parameters

- there are two versions:
  - line-symbolizer-expressions: stroke, stroke-width, stroke-opacity, offset
  - line-symbolizer-expressions-all: additionally test
    stroke-dasharray, stroke-linecap, stroke-linejoin, comp-op
    which are not supported right now
Update text-multi-layout visual tests to demonstrate placement list with layout nodes and layout/format node nesting. Add new images for line-multi-layout tests.
Added grid-reference.json files missing in 79fde58c0e1037e2494f5750eff861a51e70369e
Create tests for polygon-symbolizer, using expressions for parameters

- there are two versions:
  - polygon-symbolizer-expressions: fill, fill-opacity, gamma
  - polygon-symbolizer-expressions-all: additionally test
    comp-op which is not supported right now
Create tests for point-symbolizer, using expressions for parameters

- there are two versions:
  - point-symbolizer-expressions: file
  - point-symbolizer-expressions-all: additionally test
    allow-overlap, opacity, transform, ignore-placement, comp-op
    which are not supported right now
Merge pull request #2155 from plepe/expr-v2-tests

expr-v2: Create tests for symbolizers, using expressions for parameters
Merge pull request #2138 from MapQuest/jmh-text-layouts

Multiple text layouts in text symbolizer
restore agg polygon clipper
attempt to handle multi-polygons in shape.input
remove unused text_symbolizer.hpp/cpp
Merge branch 'expr-v2' of github.com:mapnik/mapnik into expr-v2-group-symbolizer

Conflicts:
	src/text/placement_finder.cpp
	tests/visual_tests/test.py