[typeid] Add support for spec 0.3 (underscores in type) (#318)

## Summary
TSIA

## How was it tested?
Added newest spec tests and they all pass

README.md

@@ -45,7 +45,7 @@ Latest spec version: v0.3.0
 
 | Language | Status | Spec Version |
 | ----------------------------------------------------- | ------------- | ------------ |
-| [Go](https://github.com/jetify-com/typeid-go) | ✓ Implemented | v0.2 |
+| [Go](https://github.com/jetify-com/typeid-go) | ✓ Implemented | v0.3 |
 | [SQL](https://github.com/jetify-com/typeid-sql) | ✓ Implemented | v0.2 |
 | [TypeScript](https://github.com/jetify-com/typeid-js) | ✓ Implemented | v0.2 |
 

spec/README.md

@@ -31,11 +31,11 @@ The prefix must:
 - Contain at most 63 characters.
 - May be empty.
 - If not empty:
- * Must contain only lowercase alphabetic ASCII characters `[a-z]`, or an underscore `_`.
- * Must start and end with an alphabetic character `[a-z]`. Underscores are not allowed at the beginning or end of the string.
+ - Must contain only lowercase alphabetic ASCII characters `[a-z]`, or an underscore `_`.
+ - Must start and end with an alphabetic character `[a-z]`. Underscores are not allowed at the beginning or end of the string.
 
 Valid prefixes match the following
-regex: `^([a-z]([a-z_]*[a-z])?)?$`.
+regex: `^([a-z]([a-z_]{0,61}[a-z])?)?$`.
 
 The empty string is a valid prefix, it's there for use cases in which
 applications need to encode a typeid but elide the type information. In general though,