Only fail on numpy import if using numpy

[milesgranger]

Will fix #56

Seems the FromPyObject evaluates in the order of the enum variants. Placing numpy as the last variant in BytesType will alleviate the error mentioned in #56.

• Add CI test for this.

[messense]

It works!

root@9acfadb9258b:/# pip install cramjam
Collecting cramjam
  Downloading cramjam-2.3.1-cp39-cp39-manylinux_2_17_ppc64.manylinux2014_ppc64.whl (1.4 MB)
     |████████████████████████████████| 1.4 MB 1.3 MB/s
Installing collected packages: cramjam
Successfully installed cramjam-2.3.1
root@9acfadb9258b:/# python3
Python 3.9.2 (default, Feb 28 2021, 17:03:44)
[GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cramjam
>>> compressed = cramjam.snappy.compress(b"bytes here")
>>> decompressed = cramjam.snappy.decompress(compressed)
>>> decompressed
cramjam.Buffer(len=10)
>>> bytes(decompressed)
b'bytes here'