Flurl 2.0

This release includes a major rewrite of parts of the core URL parser in support of a few new features and to address several issues and edge cases.

• NEW: Support for URL fragments (everything after #) via Url.Fragment and fluent SetFragment(string) and RemoveFragment methods on both Url and string. (#29)
• NEW: QueryParamCollection now inherits from List<QueryParameter> and therefore supports in-place sorting, etc. (#78)
• NEW: SetQueryParam(string, string, bool) overload with isEncoded argument that allows declaring the value to already be encoded, hence avoiding double-encoding. Related, if string passed to Url constructor has a query, it is assumed to be already encoded. (#56)
• NEW: Any object can be used with AppendPathSegment(s), avoiding need for explicit string cast. (#60)
• Better preservation of order when multiple values of same name appear in query.
• BREAKING: QueryParamCollection no longer implements IDictionary. It still supports some of the same methods such as ContainsKey and this[name] getter/setter, but others didn't make since as the collection is more list-like than dictionary-like.
• BREAKING: QueryParamCollection no longer has a Parse method. Query parsing can only be done by creating a Url object and inspecting the QueryParams property.
• BREAKING: string.IsUrl() extension method replaced by Url.IsValid(string) static method and Url.IsValid() instance method.
• BREAKING: Support for Silverlight 5 and Windows Phone Silverlight 8.1 has been dropped due to a few quirks they caused and apparent lack of demand for them.