Add an installation script to the repo

This updates the `make install` target and adds a new `make dist` target which
will prepare a distributable tarball with an install script. All work is based
off the equivalent rust nightly tarball and nightly installation scripts.

Closes #159
Closes #184
auto merge of #195 : alexcrichton/cargo/install, r=wycats

This updates the `make install` target and adds a new `make dist` target which
will prepare a distributable tarball with an install script. All work is based
off the equivalent rust nightly tarball and nightly installation scripts.

Closes #159
Closes #184