Ability to inject lines into existing code

[derks]

Having a larger project broken out into smaller pieces is a useful usecase for Boss. For example and existing Django project from template, and django-app template that pastes into the existing django app. Adding a line to the 'INSTALLED_APPS' list in a django settings.py would be nice. For example:

Existing project settings.py:

INSTALLED_APPS = (
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.sites',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'django.contrib.admin',
    # boss.mark:installed_apps
)

Template boss.json:

{
    "injections": [
        ["installed_apps", "'@module@.apps.@app_name@',"]
    ]
}

Using a '#boss.mark' allows us to drop a line of code after the marking point. Might be nice to make the changes, and then present a 'diff' to the user making them accept the change... but maybe that is overkill.

[derks]

This was committed, just needs documentation.