Many little changes.

Most of build.ninja file changes were based on the Makefile from
git.suckless.org/dwmstatus/tree/Makefile.

Then some renaming, prefixing the functions with bce (BitCoin-E).

Also changing it to compile with C compiler (clang) rather than C++.

Signed-off-by: Thiago Farina <tfarina@chromium.org>