Rename repository & package to 'koalas'

[w2sv]

The repository & package should be renamed to 'koalas', in order for it to align with the inflection of the package name 'pandas', which the name alludes to and is modeled after.

• Pros:
  • this OBVIOUS shortcoming would finally stop profoundly bothering me
• Cons:
  • would require all applications using this package to migrate

Hmm.