Add getPropOrError to crocks

**Is your feature request related to a problem? Please describe.**
I'm on my fourth project using Crocks and I keep reaching for the same function `getPropOrError` (and `getPathOrError`). Instead of me releasing my own library, or copy/pasting the function around I think it would be good to have this in the standard library.

**Describe the solution you'd like**
`getPropOrError :: String -> a -> Result Error b`
`getPathOrError :: [ String ] -> a -> Result Error b`

**Describe alternatives for how you do this now**
Doing a `maybeToResult` on `getProp` with an `Error` if `getProp` returns a `Nothing.`

**Code**
Do you have example code or tests in a [Repl](http://repl.it/languages/babel) for what you'd like added?

```
// getPropOrError :: String -> a -> Result Error b
const getPropOrError = curry((prop, obj) =>
maybeToResult(new Error(`'${prop}' is mandatory and missing`), getProp(prop, obj))
);
```
**Additional context**
Add any other context or screenshots about the feature request here.