[Enhancement] Added support for subdirectory-style reverse proxies (#276)

* Updated routes and other fun stuff to support reverse proxies

* Updated README

* Linting

README.md

@@ -153,6 +153,7 @@ If you change this setting and it works well for you, please leave a comment on
 | EXPOSE_FEED_ENDPOINTS | No        |                           | See [RSS feed docs](https://github.com/kieraneglin/pinchflat/wiki/Podcast-RSS-Feeds)           |
 | JOURNAL_MODE          | No        | `wal`                     | Set to `delete` if your config directory is stored on a network share (not recommended)        |
 | TZ_DATA_DIR           | No        | `/etc/elixir_tzdata_data` | The container path where the timezone database is stored                                       |
+| BASE_ROUTE_PATH       | No        | `/`                       | The base path for route generation. Useful when running behind certain reverse proxies         |
 
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