Add style setting to allow for function continuation indent width

[j4m-can]

There is no style setting to deal with continuations for a function
definition differently than other continuations. As is,
CONTINUATION_INDENT_WIDTH is uniformly applied. A new setting,
FUNCTION_CONTINUATION_INDENT_WIDTH, allows for function definition
continuations to be indented differently. For example, 8 spaces
instead of the common 4 sets off the definition continuation more
clearly. The default is to use CONTINUATION_INDENT_WIDTH otherwise.

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