Implementation for hooks

Proposed implementation for hook scripts utilising the current phpenv-hooks as mentioned in #4.

The proposal implements 2 hooks as examples.
 * hook install pre-configure  
called before `./configure` is executed
 * hook install post-configure  
called if `./configure` completed successfully.


Is this more or less what you had in mind?

We could go on from here and add install hooks for
 * pre-fetch-php
 * post-fetch-php
 * pre-buildconf
 * post-buildconf
 * pre-make
 * post-make
 * pre-install
 * post-install
 * pre-clean
 * post-clean

Coming te think of it maybe that is way too much granularity and the following would accomplish what we need with the same mount of precision.
 * pre-fetch-php
 * pre-buildconf
 * pre-configure
 * pre-make
 * pre-install
 * pre-clean
 
Maybe the pre is not required anymore simply call it make, install, clean what do you think?