Refactor default server option detection.

This refactoring moves the server detection before
the default Jasmine URL generation, since in case
of the Jasmine Gem as server, we want to have
`/` as runner url and not `/jasmine` like all the other
servers.

Fixes #120, Closes #121
Proper spec dir detection when using the Jasmine gem. (See #120)
Drop support for Ruby 1.8.7
Adding support for reporting global javascript errors
Update CHANGELOG.
Update tested Rubies.
Drop official Rubinius support.

I'm very sorry, but I'm unable to provide official support
for a Ruby interpreter that has weekly releases.

When an official Rubinius 2.0 is released, I'll bring it back.
Release 1.15.0
Upgrade Guardfile
Fix undefined global logs. (Closes #124)
Automatic detect Puma as spec server.
Add some words about istanbul Jenkins CI integration.
Reformat to fit GitHub README width.
Release 1.15.1
Update README. [ci skip]
Fix wrong description for Jenkins integration. [ci skip]
Add some words about the open commit bit. [ci skip]
Add some great projects to the alternatives section. [ci skip]

And remove unmaintained projects.
Add Teabag to the list of alternatives. [ci skip]
add dependency of tilt gem