Add some missing combinators to choosing combinator guide

[smheidrich]

Solves part of #1664

Adds:

• value
• many0_count
• many1_count
• take_while_m_n
• all_consuming
• cut
• into
• rest_len

Doesn't add:

• fill because I don't know a good way to write an example in the format of that table for this one...
• satisfy because it doesn't work with the u8 predicates like is_alphabetic etc. which makes it awkward to write an example
• iterator (not really a combinator as it doesn't return a parser)
• recognize_float and recognize_float_parts (don't see the point of those)

Someone who understands more about them could pick these up.

[Geal]

thanks!