Fix bugs in projection functions

[ziotom78]

This PR fixes issue #97 and adds several tests for the following functions:

• equiproj
• equiprojinv
• mollweideproj
• mollweideprojinv

Things to do:

• [X] Add test case to catch issue #97
• [X] Fix bugs in mollweideproj and equiproj

[codecov[bot]]

Codecov Report

Merging #99 (f698900) into master (aae0c97) will increase coverage by 0.52%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #99      +/-   ##
==========================================
+ Coverage   88.25%   88.78%   +0.52%     
==========================================
  Files          20       20              
  Lines        1320     1328       +8     
==========================================
+ Hits         1165     1179      +14     
+ Misses        155      149       -6     

Impacted Files	Coverage Δ
src/projections.jl	73.57% <100.00%> (+6.14%)	:arrow_up:

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.