Json export

Use the functions from C2C to extract the information for the atoms. Simplified printing of storage class.

Conflicts:
	driver/Driver.ml

This is a follow-up to commit 350354cb.
- Move Float.build_from_parsed to Fappli_IEEE_extra.Bparse
- Add early checks for overflow and underflow and prove them correct.
- Improve speed of Bparse by using a fast exponentiation (square-and-multiply).

This reverts commit 777566e8, reversing
changes made to daf9ac64.

Check also the discarded part of the switch statements for cases outside of an switch to bail out on earlier on unstructured switch.

Otherwise we get too many errors on glibc's standard headers.
A real error will occur when the anonymous struct/union is accessed.