Bugfix: ASFProduct.Download() filename keyword fix

[SpicyGarlicAlbacoreRoll]

• filename works with ASFProduct.download() again
• warns user if downloading multiple files and filename is specified, then ignores filename

[codecov-commenter]

Codecov Report

Merging #213 (bcac5ed) into master (e917612) will increase coverage by 1.10%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #213      +/-   ##
==========================================
+ Coverage   88.76%   89.86%   +1.10%     
==========================================
  Files          52       52              
  Lines        1958     1964       +6     
==========================================
+ Hits         1738     1765      +27     
+ Misses        220      199      -21     

Flag	Coverage Δ
unittests	89.86% <100.00%> (+1.10%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
asf_search/ASFProduct.py	94.11% <100.00%> (+34.44%)	:arrow_up: