Fix Sphinx warnings related to whitespace

[weiji14]

There's quite a few Sphinx warnings I found when working on #196. For example:

icepyx/doc/source/community/contact.rst:2: WARNING: Explicit markup ends without a blank line; unexpected unindent.
icepyx/doc/source/community/resources.rst:2: WARNING: Explicit markup ends without a blank line; unexpected unindent.
../ATTRIBUTION.rst:2: WARNING: Explicit markup ends without a blank line; unexpected unindent.
icepyx/icepyx/core/Earthdata.py:docstring of icepyx.core.Earthdata.Earthdata.login:17: WARNING: Unexpected indentation.
icepyx/icepyx/core/Earthdata.py:docstring of icepyx.core.Earthdata.Earthdata.login:18: WARNING: Block quote ends without a blank line; unexpected unindent.
icepyx/icepyx/core/variables.py:docstring of icepyx.core.variables.Variables.parse_var_list:69: WARNING: Explicit markup ends without a blank line; unexpected unindent.
icepyx/doc/source/user_guide/documentation/icepyx.rst:9: WARNING: Explicit markup ends without a blank line; unexpected unindent.

So, to make things easier to review, this PR was created separately so as to reduce the diff on #196. The main changes are:

• Ensure API docs are generated to gitignored doc/source/_icepyx folder (41eb52d)
• Fix whitespace issues in *.rst files (38bac7e)
• Fix whitespace issues in Earthdata.py and variables.py (54a420f)

[codecov-io]

Codecov Report

Merging #197 (54a420f) into development (c4439e4) will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           development     #197   +/-   ##
============================================
  Coverage        50.50%   50.50%           
============================================
  Files               17       17           
  Lines             1281     1281           
  Branches           280      280           
============================================
  Hits               647      647           
  Misses             581      581           
  Partials            53       53           

Impacted Files	Coverage Δ
icepyx/core/Earthdata.py	20.37% <ø> (ø)
icepyx/core/variables.py	8.37% <ø> (ø)

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[JessicaS11]

I thought these were all run through a linter at some point, but apparently not quite - thanks for fixing all of these whitespace issues.