Easier build: include psol headers, binary (x64/release)

To make it easier to work on this plugin, include the binary psol file and
psol headers. Also copies over a bash script from ngx_pagespeed to
make updating these headers and files easier.
This way, mod_pagespeed doesn't have to be build when compiling the plugin out of the box.

Alternatively, it is still possible to build against mps sources using 
`make -f Makefile.psol_source`