Parseable sequences with in-place reader extend

[phorward]

This makes all inline-sequences consuming input to areas with an in-place reader extend, which avoid the outer frame to break because input is not indicated to be parsed.

This program works with 9ec2b66 with input 1 2

print("stage 1 " + repr(x))
x = (Int _ Int ast("test"))
print("stage 2 " + repr(x))

Nevertheless, programs like

(Int ',' Int) | Ident   # will accept: 1,2a

will accept inputs like 1,2a, which is obviously not a wanted behavior.

Maybe it's better to introduce a new syntactic construct like a @(...) area, which creates a sequence as an in-place parse-able area.

This PR relates to #76 as initial issue.

[phorward]

As 5aab91c implements this feature well, it should be merged. I'm still a little bit odd with the syntax, especially with further visions regarding integrating parsers from modules or so.