Get rid of old/unused stuff

[wtsnjp]

I'd like to remove following things (but not so soon):

• TODO.md: we can use GitHub's issues (here) instead
• some in the doc/: I want to unify the build tool even for the documents
• all in tools/: I'm going to replace these by new scripts/tools
  • scripts for testing: we will use one of the sophisticated/well-known frameworks
  • the gen-datafiles: take into the scope of the build tool (I'm not sure about this)
  • any other necessary things? → if there are, please comment that

Some of the old scripts in this repository are unknown how to use; perhaps no one is using.

[wtsnjp]

All necessary operations (testing and generating the pre-hashed cache file) are implemented to Rakefile (and the equivalent Makefile by @norbusan; see #6), so I think now we can remove the tools dir. If there's no objection, I will do this soon. (Of course, we can revert it using git anytime if necessary)

[norbusan]

Fine with me

[wtsnjp]

All done; closing.