Option for setting pattern for duplicate function identifiers

[end2endzone]

A command line option should be created for setting the pattern for resolving duplicate function identifiers.
The current implementation uses a pattern such as _[counter] (where [counter] is replaced by the next value of a counter) to prevent duplicates.

The default pattern should be specified as _### where ### is replaced by the next counter value.

The feature should also detect how many # is used for formatting. For example with the pattern _###, when the counter is 1, the output should be _001 (note the 3 digit formatting is preserved).

Relates to #61