fix(file_list): Incorrect response after remove and add file

Remove and then immediately add same file can lead to
incorrect content in response. Because pending timeout after remove
may resolve early then file will be processed, and in response get not
processed content.
style(web-server): correct spelling in a log message.
docs(dev): Clarify git commit message instructions.
Merge pull request #1161 from eventualbuddha/clarify-commit-conventions

docs(dev): Clarify git commit message instructions.
Merge pull request #1159 from eventualbuddha/fix-typo-in-log-message

style(web-server): correct spelling in a log message.
feat(init): install coffee-script automatically

if the user initialize Karma passing a .coffee file we'll install
coffee-script and put it as a dev-dependency

Closes #1152
Merge pull request #1164 from cironunes/coffee

feat(init): install coffee-script automatically
docs(plus): Update travis details to match 0.12.
Merge pull request #1156 from Dignifiedquire/docs_travis

docs(plus): Update travis details to match 0.12.
fix(preprocessor): Throw error if can't open file
Merge pull request #1143 from keithamus/patch-1

fix(preprocessor): Throw error if can't open file
Merge branch 'pr-1088' into presubmit-master-pr-1088
chore: release v0.12.23
Merge branch 'master' into master-patched

* master:
  chore: release v0.12.23
  fix(preprocessor): Throw error if can't open file
  docs(plus): Update travis details to match 0.12.
  feat(init): install coffee-script automatically
  docs(dev): Clarify git commit message instructions.
  style(web-server): correct spelling in a log message.
  fix(file_list): Incorrect response after remove and add file