Allow the user to specify a custom script to be run in reload mode

[jryannel]

When the generator runs in auto reload mode the user should be able to specify a custom script which will be executed after the new interface files are generated.
A practical example is to generate the documentation on every change of the interface files and then auto reload the browser to show the newly generated browsers.

For Qt this would be:

qface-qtcpp --reload interface plugins --script build.sh

the script will be something like this:

export QT_INSTALL_DOCS=~/QtOpen/5.8/Src/qtbase/doc
qdoc plugin.qdocconf

And then a live reloader (using the python live reload package) should watch over the docs/html folder:

livereload docs/html

[jryannel]

With cli.py docs_serve there is now live reload support for the qface guide.

Reloading for generators is also supported through the watch module. It could be better documented t some point.

There is no support yet to call a script when the generator reloads.

[jryannel]

There is now a sh cmd to run a script. You should run it after the normal code-generation run.

from qface.shell import sh

And then use it like (assuming run runs the code generation task)

def app(...):
        run(src, dst)
        sh(cmd)