comma separator

[ieaves]

New functionality

• comma separator handling for string digits
• new utility functionality for working with missing values

Major Proposed Changes

• Integer should be a strict subset of Float

[ieaves]

@sbrugman, moved integer as a subset of float.

[ieaves]

Resolves #18

[sbrugman]

The following points may improve the PR:

• The thousands separator depends on the locale. Thin spaces, periods and comma's are all used to denote groups of thousands. If the separator configurable, then the types can be compatible with all numeric conventions.

• When the seperator is set to None (default), the type should fall back to it's current (less expensive) behaviour.