Install process improvements

[ppenzin]

This came up when I was trying to create a FreeBSD port for Neko. #84

1. Added install-strip target that is useful when there is a requirement for installing stripped binaries.
2. Unless there is a reason not to use it, mkdir -p is cleaner than getting an error, but ignoring it.

[ppenzin]

I am silly, install-strip was not needed. Will re-submit only the necessary parts later