Removing not used variable cost.

The cost is presumably calculated by looking at the salt, therefor it's
not used by the C or Java implementations.
Also removing autodetection of the cost, since that is useless, when
not using it.
Merge pull request #74 from jjoos/master

Removing not used variable cost.
`vulernability` => `vulnerability`
Merge pull request #81 from vipulnsward/fix_typo

`vulernability` => `vulnerability`
Remove links to old RubyForge page
Rename gem from bcrypt-ruby to bcrypt
Bump rake-compiler version for windows fat binaries with 2.1 support
Drop x86-mswin32-60 support

Per @luislavena on https://github.com/tjschuck/rake-compiler-dev-box/commit/ebec11e252b2adb8a932a02f7944f7c8d41825de, this was only necessary during the transition time from One-Click Ruby Installer (OCI) to RubyInstaller when 1.8.6 was released _7 years_ ago.
Add new Rubies to travis config
Merge branch 'rename_gem' of github.com:sferik/bcrypt-ruby into sferik-rename_gem-pr86

Conflicts:
	Gemfile.lock
Update Gem description to use new gem name
Clarify gem vs bcrypt() itself
Use built-in Gemspec loader
Version bump to 3.1.3
JRuby in 1.8 mode doesn't play nicely with rdoc v4
Version bump to 3.1.6
Version bump to 3.1.7