Clean up specs
Update quotes
Single => double quotes
Update Travis config
Update quotes in gemspec
Update dependencies
Remove outdated Travis config
Ignore bin dir
Discuss twelve-factor apps and reasons for use
Update copyright years
Link to license in README
Drop support for Ruby 1.9.2
Add license info to gemspec
Threadsafe ENV interaction within ClimateControl

Closes #6
Handle TypeErrors during ENV assignment

This introduces a new error, ClimateControl::UnassignableValueError,
which is raised when attempting to assign a key/value to ENV which can't
be handled.

Closes #5
Generate error message dynamically to fix spec for Ruby 1.9.3
tests: make SimpleCov optional

Skip loading SimpleCov if it is not present. This allows the tests to
run outside of Bundler if SimpleCov is not installed.