Add Explicit Support for Other File Types

[akaashdash]

Problem

10-K files and other types are not explicitly supported. They are implicitly supported, meaning that you can use a 10-Q parser on them and it will mostly work, but the top levels are not correctly identified, leading to an incorrect semantic tree. Currently provided solution is to simply let it be, but this is not good enough: https://github.com/Elijas/sec-parser-exploration/blob/main/02_other_sec_form_types.ipynb

Current State

The 10-Q parser is a bit explicitly hardcoded with not enough abstraction. This is an issue because the only major difference between documents is the level titles, so they should be easy to swap out and create support for different title groups.

To-do

Abstract out the preprocessing steps for the parsers into a different class (they should pretty much be the same for all filings). Then create lighter children classes to specify top level texts.

[hugojm]

What about adding support to other file types like FORM 8-K or FORM 20-F? I feel that should be pretty straightforward.