[FIX, DOC] Change natural log to base-ten and document output naming convention

[tsalo]

Closes None, but references #133.

Changes proposed in this pull request:

• Change natural logarithms in ALE and MKDA modules to base-ten logarithms to match NiMARE's broader convention.
• Create docs/outputs.rst to document output naming convention.
• Reorder items in documentation sidebar to better reflect their importance. Namely, the CLI is a useful item, but most users should use the Python functions directly, so the API should be at the top of the sidebar, and CLI should be at the bottom.

[codecov]

Codecov Report

Merging #333 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #333   +/-   ##
=======================================
  Coverage   82.17%   82.17%           
=======================================
  Files          37       37           
  Lines        3821     3821           
=======================================
  Hits         3140     3140           
  Misses        681      681           

Impacted Files	Coverage Δ
nimare/meta/ale.py	95.95% <100.00%> (ø)
nimare/meta/mkda.py	96.10% <100.00%> (ø)

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