const not viable yet on itemizer
add a benchmark that tests rendering with shared map - refs #2516
remove set_old_style_expression
fully disable text symbolizer for now - refs #2324
remove uneeded access to format tree
start marking as much of the text structures as const as possible - refs #2516
avoid storing evaluated text properties in text_symbolizer_properties (all style related strucures must be read-only)
make process(..) method const
    use real max glyph height

      - avoids breakage on fonts lacking an `X` glyph (#2506)
      - avoids needing to create and mutate a temporary glyph (#2516)
      - lots of minor visual changes - mostly improvements notably more correct collision boxes for lines with tall glyphs
update a few expected images in python tests
update expected grids
update expected agg images
update expected cairo images
Merge pull request #2519 from mapnik/max-glyph-height2

use real max glyph height
reduce pointer usage in text renderer - refs #2516
cairo: avoid creating evaluated_format_properties_ptr on stack
make cairo_context.add_text more like agg::text_renderer
remove unused (after 8bc7a56cda204e9e) font_face::char_height_
cairo text rendering: avoid double call of set_character_sizes for text and halo
drop unwise glyph_info caching - reverts 99a46f6910 - re-opens #2334
give glyph_info better ctor