Update AS instrumentation to match RSolr 1.0.7

Improve instrumentation log readability

Quote string values and remove query escaping.
Merge pull request #377 from felixbuenemann/fix-activesupport-instrumentation

Fix ActiveSupport instrumentation
Update travis and gemfiles so now runs the latest Rails version in all cases
Merge pull request #428 from sunspot/test-with-latest-rails

Update travis and gemfiles so now runs the latest Rails version in all cases
Dropped support for rails 2.x. Added support for Rails 4.

Updated to rspec 2.14.0. Updated specs to work with Rails 4. Added
Rails 4 to Travis config. Bumped version to 2.1.0