Serenity: LibM: Add moar math for Janet Lang

[The-King-of-Toasters]

I'm trying to port The Janet Language, and it creates wrappers for mathematical functions we don't have. These include:

• [x] acosh
• [x] asinh
• [x] atanh
• [x] exp2
• [x] expm1
• [x] cbrt
• [ ] trunc, implemented but not defined in math.h.
• [x] gamma
• [x] log1p
• [x] erf
• [x] erfc
• [x] hypot
• [ ] nextafter

We're also missing some macros:

• [x] INFINITY
• [ ] isnan and isinf. The rest of the fpclassify functions would be nice too.

[bugaevc]

OMG, a language named after Janet! Yes please, and we have to get the port working :)

[alimpfard]

And here we see @bugaevc fanboying over something (admittedly nice).
meanwhile here I am liking its lispiness more than the character it references...