Update Travis ci tests

Remove rails master, add rails 4-0-0
Merge pull request #240 from huoxito/revert-dot-scaping

Revert dot scaping in SQL values
Update README

Add Gemfile instructions for Rails 4 branch, and update code examples
to Ruby 1.9.3 / 2.0.0 hash syntax.
Remove Rails 4-0-0 tests from travis-ci

The 4-0-0 branch no longer exists in the Rails repo.
Travis-ci: Temporarily comment-out "ruby-head" test

Travis is currently unable to load from rubygems.org. Tested with ruby
2.0.0-head today; same issue.
README: Harmonize Gemfile instructions with the master branch.
Update Gemfile: Rails 4-0-stable default, new hash syntax,

and remove the polyamorous gem (which is already specified in the
gemspec).
Default_scope without a block is deprecated in Rails 4
Travis-ci remove older rubies and rails.
Relation#all is deprecated. Use Ruby 1.9 hash syntax.
Travis-ci: concentrate on Rails 4 & Ruby 2.0.0, 1.9.3

as latest changes for Rails 4.1 are incompatible with Rails 3.
Force strict dependency on AR and AP versions of ~> 4.0.0
Fixes #260
Remove deprecated ActiveSupport::Benchmarkable#silence