Add cmake file to use cmake to build libTonicLib

[mantaraya36]

No description provided.

[LB--]

Relation to #255 ?

[morganpackard]

Thanks @mantaraya36. As @LB-- points out, we already have one cmake PR in the works, by @andik. I haven't used cmake much before and am trying to understand how people use, and prefer to use Tonic. I generally include the Tonic XCode project as a subproject in XCode. In some ways, I prefer what you've submitted here to what @andik has does, since it's just the addition of one file, in its own place, adding cmake as just another build option.

[andik]

I just need to say that this for example doesn't comile the examples letting alone the user who wants to try out these.
But it installs the library which really is a great plus.
@mantaraya36 could you also provide a FindTonic.cmake?