0.3.1

• Ability to set additional capabilities for all browsers, using
  capabilities option in .gemini.yml:

  capabilities:
    option1: value,
    option2: value

• Non-existent directories, passed to gather and test commands will
  be filtered out

• If fatal error occurs, gemini will always exit with 1 status code

• If test fails or state error occurs, gemini will always exit with 2
  status code.

• When gemini is unable to launch browser, more clearer error message
  will be displayed.