Missing bracket. Refs #254
Merge branch 'missing-bracket'
Fix test for missing brackets
Fix repeated comments in selectors. Fixes #260
Add failing identity nesting case, refs #262
Quote ampersend chars in XML text. Closes #263.

Includes testcase.
Quote all needed XML chars. See #263.

Includes testcase.
Fix #262,

when selectors are exactly the same, still push them into the list.
Tolerate commas in values. Fixes #266
Tolerate single-stop colorizers. Fixes #251
Do not output references to empty styles. Fixes #244
Merge pull request #265 from strk/master-quote-amp

Quote ampersend chars in XML text. Closes #263.
Do not unnecessarily escape < and chain replacements
Support variable-length arguments in functions with -1
Merge pull request #271 from mapbox/colorize-alpha

Support variable-length arguments in functions with -1
Handle errant zoom-as-field better. Fixes #269.
Fix dimension.js code style
Refactor physical unit support
Dimensions.
Prevent image filter duplication. Fixes #270