Support string format and duplication using AIM datatype formatting.

The existing function aim_fstrdup() is convenient, but does not allow
for AIM custom datatypes in the format string.

The new functions aim_dfstrdup() and aim_vdfstrdup() allow for
AIM datatype formatting in the input.
Merge into master from pull request #17:
Support string format and duplication using AIM datatype formatting. (https://github.com/floodlight/infra/pull/17)