Update version number to 0.9.9.3
Wrap Idris in an ErrorT

This is the first step in getting error reflection to work. The next is to
centralize the error handlers.
Make "Stale IBC" use the new error system
Update compiler to use new error handling
Use the ErrorT failure functions and attempt to preserve error structure
Merge pull request #539 from david-christiansen/errort

ErrorT
Add missing pattern
add myself to CONTRIBUTORS
Merge pull request #540 from reynir/patch1

Add missing case in the pretty printer
Added myself to contributors
Added "if_valid" syntax rule for possibly failing Effects

Allows branching based on whether an effectful operation returning
Either l r succeeds (l failure, r success) and updating the resource
accordingly.
Merge pull request #541 from ahmadsalim/feature/mecontributors

Added myself to contributors
Update CHANGELOG