* Change master seed to secret in most places, ''t'' to ''k'' and other term fixes
* Replace deleted linebreak, delete vestigal oxford commas
* errors->random errors, fix newlines, vector5: secret seed->codex32 secret
reduced the heading level of checksum and error correction to make the table of contents easier to parse.
Moved Master seed Encoding to be below Unshared Secret.
* BIP93: change codex32 characters to bech32 characters
* Fix hrp length off by 1 bug. Refactor validity condition to read easier.
