Addressable 2.1.0

Addressable is a replacement for the URI implementation that is part of Rubys standard library.
Addressable adds support for URI and IRIs templates and more closely conforms to the relevant RFCs.
NOTE: Addressable is licensed and distributed under the terms of the MIT/X Consortium License.

Enhancements
- refactored URI template support out into its own class
- removed extract method due to being useless and unreliable
- removed Addressable:URI.expand_template
- removed Addressable:URI#extract_mapping
- added partial template expansion
- fixed minor bugs in the parse and heuristic_parse methods
- fixed incompatibility with Ruby 1.9.1
- fixed bottleneck in Addressable:URI#hash and Addressable:URI#to_s
- fixed unicode normalization exception
- updated query_values methods to better handle subscript notation
- worked around issue with freezing URIs
- improved specs