Remove extensibility tests. Ohm::Model::PureRuby not exist.
Remove unused files/directories from .gitignore.
Remove rubygems require. Ohm supports Ruby >=1.9.
Encourage users to use a symbol/string as model references.
Merge pull request #123 from frodsan/use_symbol_or_string_instead_of_constant_with_model_references

Encourage users to use a symbol/string as model references.
Merge pull request #119 from frodsan/remove_old_tests

Remove extensibility tests. Ohm::Model::PureRuby not exist.
Merge pull request #122 from frodsan/remove_rubygems_require

Remove rubygems require. Ohm supports Ruby >=1.9.
Merge pull request #121 from frodsan/remove_old_dirs_from_gitignore

Remove unused files/directories from .gitignore.