More flexibility in wavelets

[msyriac]

This allows you to pre-filter maps sent into map2wave, which saves 2 SHTs.
It also allows you to specify wavelet coefficients that should be skipped, saving several alm2map operations if you don't need wavelet maps at all scales.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 19 lines in your changes missing coverage. Please review.

Project coverage is 40.36%. Comparing base (c0b552b) to head (c693e5f).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pixell/wavelets.py	0.00%	19 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #270      +/-   ##
==========================================
- Coverage   40.40%   40.36%   -0.05%     
==========================================
  Files          28       28              
  Lines        9822     9833      +11     
==========================================
  Hits         3969     3969              
- Misses       5853     5864      +11     

Flag	Coverage Δ
	40.36% <0.00%> (?)

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