Update gemspec styling
Add thor and bin/appraisal executable
Setup RSpec to support acceptance testing
Add base spec for `appraisal generate`
`appraisal generate` is now working
Add default task, so `bin/appraisal` => `generate`
Speed up some test by build gem only once
Fix cucumber test failure
Adds `appraisal install`
Do less RSpec overriding
Auto relative-ize generated gemfiles

Fixes #49 and closes #50
Make `appraisal` runs install command instead
Make Thor exit with nonzero status code on failure
Make Travis build against more branches and rubies
Add `appraisal clean` command
Allow failures on JRuby and ruby-head for now
Add `appraisal APPRAISAL_NAME COMMAND` command
Add `appraisal COMMAND` to run the command`
Merge `APPRAISAL [APPRAISAL_NAME] COMMAND`

This prevents the need to have a description for each appraisal
subcommand as we'll add "Usage" section on top of the help command.
Add useful help message to `appraisal help`