SoftFloat: added sin, cos and docs (#9329)

* softfloat: comparison operators made inline, min() max() eps() isSubnormal() added

* softfloat: get/set sign/exp

* softfloat: get/set frac

* softfloat: tests rewritten with new tools

* softfloat: added pi(), sin(), cos()

* softfloat: more comments

* softfloat: updated sincos arg reduction

* softfloat: initial tests for sincos added

* softfloat: test works, code cleanup is pending

* softfloat: sincos argreduce rewritten

* softfloat: sincos refactored and simplified

* softfloat sincos: epsilons calibrated

* softfloat: junk code removed from tests

* softfloat: docs added

* inline comparisons undone; warning fixed