Refactor parser compile functions

[yui-knk]

Refactor parser compile functions to reduce the dependence
on ruby functions.
This commit includes these changes

1. Refactor gets, input and gets_ of parser_params

Parser needs two different data structure to get next line, function (gets) and input data (input).
However gets_ is used for both function (call) and input data (ptr).
call is used for managing general callback function when rb_ruby_parser_compile_generic is used.
ptr is used for managing the current pointer on String when parser_compile_string is used.
This commit changes parser to used only gets and input then removes gets_.

2. Move parser_compile functions and gets functions from parse.y to ruby_parser.c

This change reduces the dependence on ruby functions from parser.

3. Change ruby_parser and ripper to take care of VALUE input GC mark

Move the responsibility of calling rb_gc_mark for VALUE input from parser to ruby_parser and ripper.
input is arbitrary data pointer from the viewpoint of parser.

4. Introduce rb_parser_compile_array function

Caller of rb_parser_compile_generic needs to take care about GC because ruby_parser doesn’t know
about the detail of lex_gets and input.
Introduce rb_parser_compile_array to reduce the complexity of ast.c.