Fix route to get schema for Rails 4.1.2

Due to changes in Rails 4.1.2, slashes in a path generated by
json_schema_rails url helper were escaped to '%2F', which is not
comfortable for nested schema names.

To avoid the escaping, we need to use wildcard segments ('*foo') to
express a parameter of schema name. So stopped using "resources" routing
and uses "get" with "as" parameter for url helpers.
Merge pull request #3 from kotas/fix-schema-url-helper

Fix route to get schema for Rails 4.1.2