Fix doc name, specify throws in two functions

[robertkleffner]

Reading through and trying to grok some aspects of HEALpix, I discovered one function in nside.jl had an incorrect function and parameter names in the documentation.

[codecov[bot]]

Codecov Report

Merging #110 (885f8c4) into master (1719ebe) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #110   +/-   ##
=======================================
  Coverage   91.08%   91.08%           
=======================================
  Files          20       20           
  Lines        1447     1447           
=======================================
  Hits         1318     1318           
  Misses        129      129           

Impacted Files	Coverage Δ
src/nside.jl	100.00% <ø> (ø)

[ziotom78]

Thank you so much, @robertkleffner , I love when users submit pull requests to fix things by themselves! Much appreciated!