expose API to extract find_package-like CMake function calls

[mikaelarguedas]

this allows for reuse in this package and for extension wanting to leverage that feature (e.g. https://github.com/eProsima/Fast-RTPS/pull/207#issuecomment-383248609)

[mikaelarguedas]

spell checker was not happy with regex. It may be worth adding it to a whitelist (this one?) if we think that's something we'll use "regular"ly

[dirk-thomas]

After talking offline I pushed a modified patch which keeps the pattern, the regex evaluation and the extraction of the desired capture groups within a single function to avoid exposing too much information.

[mikaelarguedas]

lgtm, We could reuse that regex to find the project name. But as discussed offline we can do that separately.

Travis is unhappy though, looks like an install fluke