Cross-type conversion, cached base functions, Contexts mutable once, casting FormatOrderX without templates, casting Permute outputs is optional

[AmroAlJundi]

Applied changes presented in issues #147 , #177 , #168, #198 and #193. More specifically:

• Added cross-data type conversion for format objects.
  • Added a functor for type conversion to FormatOrderTwo and FormatOrderOne that is templated on the output types (functor rather than function so we can partially initialize it). The generic functor does not compile.
  • For each type-convertible class, I specialized the TypeConverter function for that class and implemented it.
  • Added a Convert function that takes a format class and types to FormatOrderOne and FormatOrderTwo that uses the functors above.
  • Added so many tests.
• Made context data members inside formats one-time settable -- once they are set, any consequent attempts to change them will throw an exception.
• Added cached versions of ReorderBase and GraphFeatureBase functions.

[AmroAlJundi]

Will add two additional features over the PR.

[ardasener]

There is an issue related to As -> AsAbsolute conversion in docs (for example see line 216 in the getting_started/usage page). I am approving this PR now since we will likely do a major overhaul to the docs and these problems can be fixed there.