Complete rewrite of package to use EDGAR Search API

[jadchaar]

Complete rewrite of package to use the EDGAR full-text search API as the new filing retrieval method.

Closes: #47
Closes: #31

[codecov]

Codecov Report

Merging #52 (3827d08) into master (0431060) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #52   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines          100       141   +41     
  Branches        16        25    +9     
=========================================
+ Hits           100       141   +41     

Impacted Files	Coverage Δ
sec_edgar_downloader/Downloader.py	100.00% <100.00%> (ø)
sec_edgar_downloader/_constants.py	100.00% <100.00%> (ø)
sec_edgar_downloader/_utils.py	100.00% <100.00%> (ø)
sec_edgar_downloader/_version.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0431060...3827d08. Read the comment docs.