First version of makefile - handle building of the library itself.

TODO: Handle demo-program as well.
Add header as dependency of object file. Also change to use c++ to compile file.
Add sub-directory makefile, due to 6a55712a.

Commit 6a55712a break old Makefile, so I move old Makefile inside library/ and write new top-level Makefile. Note that the top-level Makefile contain the rule for demo-program too, but the Makefile for demo-program isn't written yet.
Edit .gitignore file to exclude result of demo-program.
Write Makefile for demo-program.
Edit Makefile to be generic and enable demo-program.
Merge branch 'create-makefile'

This will make the project more useful, and will make whole build process lot more easier.