v0.2.1

Muon v0.2.1

Diff since v0.2.0

Merged pull requests:

• Avoid type promotion in increment/decrement (#27) (@dmbates)
• Use PooledArrays for unordered categorical vectors (#28) (@dmbates)

Closed issues:

• New release? (#25)
• Use PooledArrays.PooledArray for unordered categorical columns (#26)