Remove the BCL Parse/TryParse/ToString(...) static format/parse methods

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See proposal in https://groups.google.com/forum/#!topic/noda-time/cFYJlJfITOQ.  
In summary: we currently have two ways to format and parse text: the 
pattern-based API, which is strongly-typed and pretty straightforward, and the 
BCL IFormatInfo-based API, which is underdocumented and confusing.  (There are 
other problems as well; see the post.)

Assuming no objections, we should remove all the static Parse/TryParse methods 
and trim down the ToString overloads to two: the parameterless one and the one 
used for IFormattable.

We'll also need to update the user guide.

Original issue reported on code.google.com by malcolm.rowe on 14 Jul 2012 at 9:05