Fixed indentation.
Updated TODO list.
Updated some examples.
Major refactoring with focus on coinductive types.

Added 'mk#', 'is#', 'un#', and 'index'.
Removed unnecessary language extensions.
Refactored 'Data.Frame', added documentation, and removed useless
code.
Renamed 'Data.FrameEnv' to 'Data.FrameTree' and refactored code.
Added 'ModuleSymbol' which allows a simple implementation of modules
with proper nesting.
Removed unnecessary 'Data.Stx' constructors which were replaced with
functions.
Simplified 'Linker' using 'moduleId' names in each module.
Removed 'Macros' file (finally :)).
Added coinductive types without typechecking.
Fixed 'uses' in 'Renamer'.
Fixed command 'showRenamed'.
Removed useless code.