At this point all of the jss::* names are defined in the same
file. That file has been named JsonFields.h. That file name
has little to do with either JsonStaticStrings (which is what
jss is short for) or with jss. The file is renamed to jss.h
so the file name better reflects what the file contains.
All includes of that file are fixed. A few include order
issues are tidied up along the way.
Avoid custom overflow code; simply use 128-bit math to
maintain precision and return a saturated 64-bit value
as the final result.
Disallow use of negative values in the `fee_mult_max`
and `fee_div_max` fields. This change could potentially
cause submissions with negative values that would have
previously succeeded to now fail.
