Using Edgar Tools instead of custom solution.

[josephkern]

Building a custom solution for Edgar parsing for the last few days, I found Edgar tools and migrated immediately. SEC Edgar data is deceptively simple at first and then gets progressively more complex with too many edge cases to count.

Once I've built around Edgar Tools a bit more, I'll submit upstream PRs. :-)

Thanks!

Migration summary:

• Lines deleted: roughly 2,000 (custom parsers + their tests)
• Lines added: roughly 900 (adapter + tests)
• Net: ~1,100 fewer lines, plus Form 4 goes from NULL-stubs to real transaction data, 13F
  handles pre-2012 formats, and the "accurate over complete" XBRL discipline is preserved
  via derive_period_type living in the adapter.