Updated Makefile, builds rpm in local directory

The rebuild instructions (from README.md) aren't correct for CentOS, which places the `rpmbuild` directory in the user's home directory. The resulting RPM is placed in `~rpmbuild/RPMS/noarch/`. On Fedora (Rawhide), the output directory seems to `/rpmbuild/RPMS/noarch/` -- also different from documented. To alleviate the trouble new users might have with this, I rewrote the Makefile.

Builds will now occur in the yumbootstrap build directory under `rpm-build`. For convenience, both src.rpm and noarch.rpm will be copied to the top of the build directory. A build and install is simplified to:

```sh
>make rpm
>sudo make install
```
Followed by cleanup:

```sh
>make clean

-or- To remove intermediate build files but preserve src.rpm and noarch.rpm in the top directory...
>make mostlyclean
```

The old `make install-notmodule` remains. This has been tested on CentOS 7 and Fedora Rawhide.