docs: improve doc generation and contents

docs(requirements): create a separated req file

docs(project): improve overall project docs.

docs(create_context): document options for context

refact(check): improve error check options support

feat(parse): improve parsing

docs(typos): fix typos using enchant+pylint

fix(check): prevent misterious description error

refact(minor): improve defintions and utils

refact(check): always return tuple for consistence

feat(walk): add function to traverse tree

feat(parse): add parse function (str => AST)

chore(ci): ignore sort order of docs/conf.py

refactor(modules): extract builder and reorganize

fix(wrapper): fix wrapper issues with `comment`