Adding 2 new combinators

[Javran]

would like to see these two combinators in parsec :)

• countUpTo n is the equivalance of {,n} in regular expressions
• countFromTo m n is the equivalence of {m,n} in regular expressions

[mrkkrp]

@Javran, I like the idea. I will include this in Megaparsec, see mrkkrp/megaparsec#17. Not sure it will get any response here, but I would advice the following improvements for this PR:

• define countUpTo in terms of countFromTo: countUpTo n = countFromTo 0 n, not other way around, because countFromTo is obviously more general of the two;
• you have a typo in description of countUpTo: @countUpto n p@ ...;
• please rewrite description of countFromTo;
• better name variables in countFromTo as in description, i.e. m n p, not l r p, this will make the function easier to understand for readers of your code.

[hvr]

Note to myself, count and count' now live in http://hackage.haskell.org/package/parser-combinators-0.2.0/docs/src/Control-Applicative-Combinators.html#count

@mrkkrp am I right to assume that parser-combinators can be combined with parsec? or is there still some incentive to implement count/count' natively for parsec?

[mrkkrp]

Yep, all combinators from parser-combinators can be used with Attoparsec, Parsec, Megaparsec, and probably Trifecta too.