Use Lrama LALR parser generator instead of Bison
I want to propose to use Lrama LALR parser generator instead of Bison.
https://github.com/yui-knk/lrama is a pure ruby parser generator which accepts Ruby's "parse.y" and generate compatible "parse.c" file.
By this change, we never depend on Bison whose version is different for each environment.
Future improvement, like Nonterminal attributes and so on, will be discussed other tickets.