Write new formatting engine

[rjmholt]

PSSA2 currently only has an analyzer. It should also have a formatter.

In particular, the API should allow objects to implement an abstract class that doesn't emit diagnostics, but instead contributes edits to a formatting buffer.

Rules should be able to provide an implementation for this also by implementing an API that provides an instance of the required abstract class.

Requirements are:

• Run as many formatters over the script as it can at once
• When formatters want to overwrite the same extent, the largest wins
• Attempt to run until no more formatters have edits to make, up to some maximum number of runs
• Formatters should reuse the rule configuration system

[bergmeister]

What if one formatter makes one change? You will have to translate the offset then (this is expected and should happen anyway, just hasn't been implemented atm). Currently re-parsing and reanalysis happens and even with implementing translation that would still be required when an overlapping extent is modified. I don't see it as a problem that the formatter re-uses the concept of a DiagnosticRecord.