move contrib's docs into thir directories
grammer fix
Merge branch 'master' into doc

Conflicts:
	CMakeLists.txt
move docs to contribs
fix link
update betz (to implement pickle) and add its test
update build.sh
add generated contrib.rst
You need to run `make doc` before you commit when you have edited docs under contrib/.
update .gitignore
fixed #232
Merge branch 'master' of github.com:picrin-scheme/picrin
Merge branch 'doc'
Revert "update betz (to implement pickle) and add its test"

This reverts commit ae450b95b9bddc7339343e085afe586d1d871e76.