Further improvements to descriptions/config

- Allow alt. keys to be used in config (eg. `eka` or `eka_portal` => `aryion`) and refactor out this logic
- Refactor duplicated config parsing logic
- Add `-D --define-option` args for script invokation conditions
- Allow `-f --file-path` arg to be used several times
- Allow `-f --file-path` to be used without setting up an input story or description

sites.py

@@ -0,0 +1,13 @@
+import itertools
+import typing
+
+SUPPORTED_SITE_TAGS: typing.Mapping[str, typing.Set[str]] = {
+  'aryion': {'aryion', 'eka', 'eka_portal'},
+  'furaffinity': {'furaffinity', 'fa'},
+  'weasyl': {'weasyl'},
+  'inkbunny': {'inkbunny', 'ib'},
+  'sofurry': {'sofurry', 'sf'},
+}
+
+INVERSE_SUPPORTED_SITE_TAGS: typing.Mapping[str, str] = \
+  dict(itertools.chain.from_iterable(zip(v, itertools.repeat(k)) for (k, v) in SUPPORTED_SITE_TAGS.items()))