Support for separator character '_'

[ideasman42]

Some languages support using underscores as separators, so 16_777_216 is evaluated as 16777216.

This task proposes to optionally support these characters;

This would add a custom variable: evil-numbers-separator, values would include:

• nil no support, numbers would be treated as separate values (current behavior).
• t support evaluating numbers using these separators, keeping the separators in the incremented number.
• '(3) would add a separator every 3 characters. '(3 2) would add every 3rd then 2nd... and so on.

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Notes:

• VIM does not support this functionality as far as I know.
• Since support for this is language spesific, users would set this as a buffer local variable.

[ideasman42]

This is implemented in master.