Conditional import of cmisc to fix readthedocs

[msyriac]

Fixes #226

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (6e7ae24) 44.80% compared to head (2159465) 44.81%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #234 +/- ## ======================================= Coverage 44.80% 44.81% ======================================= Files 33 33 Lines 10633 10636 +3 ======================================= + Hits 4764 4766 +2 - Misses 5869 5870 +1 ``` | [Files](https://app.codecov.io/gh/simonsobs/pixell/pull/234?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=simonsobs) | Coverage Δ | | |---|---|---| | [pixell/curvedsky.py](https://app.codecov.io/gh/simonsobs/pixell/pull/234?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=simonsobs#diff-cGl4ZWxsL2N1cnZlZHNreS5weQ==) | `62.04% <75.00%> (+0.01%)` | :arrow_up: |

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