The readers previously assumed that CRs had been filtered
from the input. Now we strip the CRs in the readers themselves,
before parsing. (The point of this is just to simplify the
parsers.)
Shared now exports a new function `crFilter`. [API change]
And `tabFilter` no longer filters CRs.
Formerly tracing was just log messages with a DEBUG log
level. We now make these things independent. Tracing
can be turned on or off in PandocMonad using `setTrace`;
it is independent of logging.
* Removed `DEBUG` from `Verbosity`.
* Removed `ParserTrace` from `LogMessage`.
* Added `trace`, `setTrace` to `PandocMonad`.
