Generalize the few functions that are not common across all the core integer modules

[brson]

The uint/int/i8 etc modules mostly share the same code but there are a few functions that are still specific to a single module. It should be possible to move these to the int-template or uint-template module as appropriate so they can be used for all integer types.

These are they:

• int::{ hash, parse_buf, from_str, to_str, str, pow }
• uint::{ div_ceil, div_round, div_floor, hash, iterate }
• uint::{ next_power_of_two, parse_buf, from_str, to_str, str }
• u64::{ to_str, str, from_str }

[graydon]

This feels nearly-done to me, you agree?

[Aatch]

Is this done now? With the extensive re-working of std::num we don't even have [u]int-template any more.

[thestinger]

Instead of the template we have macros generating non-generic functions now.

[thestinger]

There's no longer a lack of code reuse, but definitely a lack of generic functions rather than generated code. These are often very hard to write without missing corner cases, so they can be tackled individually.