CLN: template hashtable.pyx

[jreback]

use Tempita support to provide templates for routines in hashtable.pyx. Lots of duplicated code by dtype that can easily use fused types, so code generation is needed. Following along the lines of #13716 would be nice.

[sinhrks]

I'm going to handle. What do you think adding other dtypes like int32, etc (related to #701?).

[jreback]

yes int32/float32 are reasonable (but could be hone later)