d2a597c90d unit: Group re-exports (Tobin C. Harding)
d242125ae4 units: Fix error re-exports (Tobin C. Harding)
Pull request description:
First patch is the meat and potatoes, second one is just a trivial refactor to the same code, done separately so as to make the changes in the first patch more clear.
From patch 1
```
units: Fix error re-exports
Currently we re-export two error types at the crate root, this is
surprising because:
- Why not none or all the rest?
- Why these two?
Observe that the `ParseIntError` is special in that it is used by
other modules so its good to have at the crate root (other errors are
expected to be used with a module prefix eg, `amount::ParseError`).
There is no obvious reason why `ParseAmountError` is re-exported.
Comment and doc inline the `ParesIntError`, remove the re-export of
the `ParseAmountError`.
```
ACKs for top commit:
apoelstra:
ACK d2a597c90d
Tree-SHA512: 38d3f590357e66d07cbd7fedff134c39e0920e076ea99cb34ba276749a14695d428345d7b0f9ec8222f7899cb57e7c97068d3b6e7b2a9be25a0278e0a1abf762