Merge tag '0.4.0' into develop

0.4.0
Add installation instructions of MELPA and el-get.
Add gittip badge.
An initial attempt to run tests on Travis and Vagrant.
Add Travis badge.
Update README.
Add 'now' command.

See #9
Add gitter badge.
New screenshot with the 'now' option.

See #9.
Change the color of gitter badge.
Merge pull request #11 from yasuhito/feature/now

Feature/now
Update changelog.
Minor rewording.
Version bump.
Merge branch 'release/0.5.0'