* `Result` refresh
* add full support for `Result[T, void]` (aka `Opt[T]` aka `Option[T]`)
* expand tests
* add `flatten`, `filter` of `Option` fame
* add `tryError` that raises a regular exception when result holds a
value
* fix `$` to print `ok`/`err` in lower-case, like the functions that
created the result
* add `orErr` that collapses all errors to a single value of a
potentially different type - useful when translating errors between
layers
* `capture` should work with `CatchableError`
* remove `Defect`-dependent tests
* Update stew/results.nim
* avoid redundant error message when converting error to string
* avoid multiple evaluation in `valueOr`
* add `unsafeError` to match `unsafeGet`
* let `valueOr` evaluate a block
* add `errorOr` to mirror `valueOr`
It turned out that Nim's Option type is broken for `not nil` and
`requiresInit` types. It will report an udesired warning due to
the way `none` is defined. The `Result` type doesn't suffer from
this problem, so I've transitioned some APIs in NBC to use the
new `results.Opt[T]` type (alias of `Result[T, void]`).
Perhaps we should renamed `Result` to `Res` to make the naming
more consistent and to allow the code to more easily fit in the
80 character per-line budget.
