Added an arity trait
Can deduce arity of pretty much every callable except templated ones
Added template-indexable placeholders
Added a missing header
Added a range sequence builder
Added some sort of curry helper
Fixed composition
Should now work with different arities
Added a convenient make_composable
This allow composition of custom functors / functions
You can even make templated callables composable by manually specifying their arity
Removed composition tests for now
I will have to rewrite them properly according to the API change