Fix 'notFollowedBy'

This bug (or undocumented behavior?) also exists in original Parsec
(see https://github.com/aslatter/parsec/issues/8).
Add test for 'notFollowedBy'
Add test for 'manyTill'
Refine 'manyTill'
Refine 'sepEndBy'
Update TODO
Add synonyms

‘try’ for ‘attempt’ and ‘void’ for ‘nullify’
Add methods of parser

They can be used like syntactic sugar of functions in ‘prim’ and
‘combinator’