Terse function names are used to make usage not stutter. For example:
```go
err := error.Forbidden("you shall not pass")
```
At the moment they are all the same fundamental `MatrixError` type. This will
be bad if we ever want to `switch` based on the kind of error. I'm hoping we
won't ever need to introspect into errors like this: ideally these errors would
be created purely for immediately being returned in an HTTP response.
`MatrixError` implements the `error` interface.
Robert Swain
Kegsay