Update encoded format to match the size of "q"

| Q  | A
| --- | ---
| Bug fix? | yes
| New feature? | no
| BC breaks? | no
| Deprecations? | no
| Issues fixed by this | #2 

Fixes #2 by calculating the size of `q` of the associated curve before exporting the encoded value of a point.

# Tasks
- [x] Write more test cases for valid examples
- [x] Changelog updated
- [x] Usage/Documentation updated
- [x] Tests pass
- [ ] ACK from other developers