Move Lucky specific methods to a separate module

[paulcsmith]

Move these...

• https://github.com/luckyframework/lucky_flow/blob/b14b8645eb30d78d371c30c3f9a1be15dd403d01/src/lucky_flow.cr#L24-L37
• https://github.com/luckyframework/lucky_flow/blob/b14b8645eb30d78d371c30c3f9a1be15dd403d01/src/lucky_flow.cr#L59-L75

Into a module called LuckyFlow::LuckyHelpers

Will likely require splitting spec into Lucky specific tests.

There should also be a flag similar to what is done in Carbon: https://github.com/luckyframework/carbon/blob/master/README.md#development that let's you run specs with and without Lucky to ensure that it works for no matter what

[jwoertink]

One question here is, would the lucky specs be default, or if this is geared for any framework, then would you want something to wrap the spec call like ./bin/spec which runs crystal spec -D include-lucky or whatever?