Empty enums generate error

### Expected Behaviour

To be able to leave an empty enum in the code, e.g.:
```
enum Options {
// add your amazing option here
}
```
Why would I do this? Perhaps I have a bunch of code dependent on the enum (but not specific enum values) that I'm not ready to delete, because I expect to introduce different values into the enum in the future.

### Actual Behaviour

Empty enums generate an error:
```
ERROR:root:FAILED: Hyde-validate for //options.hpp
ERROR:root: stdout:
ERROR:root: stderr: ///options.md: extraneous file
Error: YAML documentation failed to validate.
```
If `options.md` is removed, a different error is generated:
```
ERROR:root:FAILED: Hyde-validate for //options.hpp
ERROR:root: stdout:
ERROR:root: stderr: Error: YAML documentation failed to validate.
```

### Reproduce Scenario (including but not limited to)

#### Steps to Reproduce

Create an empty enum and run hyde

#### Platform and Version
Mac OS.

#### Sample Code that illustrates the problem
```
enum Options {
// add your amazing option here
}
```
#### Logs taken while reproducing problem