Create system for plugin modules to tie into specified hooks

[ewels]

Could create another setuptools entrypoints class (multiqc.hooks.v1?) that could create a list of functions to run at different points in the code.

[ewels]

Refactoring issue to be more specific, now that #61 has covered some of the original scope.

[ewels]

A load of pseudocode to pen down roughly how I see this working:

Plugin setuptools code:

 entry_points = {
  'multiqc.hooks.v1': 'mypluginhooks = myplugin.hooks'
}

Then in myplugin:

def hooks(trigger):
  return triggers.get(trigger, None)

triggers = {
  'click' : click_trigger,
  'modules_start': modules_start_trigger,
  'modules_end': modules_end_trigger
}

def click_trigger():
  """ Could add some extra click arguments here """
  pass

def modules_start_trigger():
  """ Runs before modules start """
  pass

def modules_end_trigger():
  """ Runs when modules finish """
  pass

Finally, in multiqc:

# Load the hooks
hook_functions = []
for entry_point in pkg_resources.iter_entry_points('multiqc.hooks.v1'):
  hook_functions.append(entry_point.load())

# Function to run the hooks
def multiqc_trigger(trigger):
  for h in hook_functions:
    h(trigger)

# .. do some stuff, trigger the hook ..
multiqc_trigger('modules_end')