Bugfixes and small improvments to the parsec adapter

[emmabastas]

This PR fixes two bugs found in #740 and adds some other improvments.

The three important changes are:

• The initial indentation level is set to 1 instead of 0. Row and column numbering starts at 1 so initial indentation now matches that. (see 425321d)
• Text.Parsec.Indent.withPos restores to the previous indentation before calling a continuation. (see 26dc657)
• Text.Parsec.Pos.updatePos can now handle tabs. (see 06c17f3)

Some less important changes:

• Text.Parsec.Combinator.eof gets an implementation exactly matching the parsec implementation.
• Text.Parsec.Combinator.anyToken gets an implementation (eof needs it)
• Text.Parsec.Prim.(<?>) gets an actual implementation instead of just leaving the parser unchanged, although the implementation might not exactly match the parsec behaviour.

It looks to me like the test suite passes with these additional commits.