Add isValid(), fix security issues in dependency (#11)

* fix security issues in dependency with npm audit fix

* added: isValid()

* case insensitive. remove redundant import.

* case insensitive. remove redundant import.

* Make isValid more efficient

Co-authored-by: Perry Mitchell <perrymitchell@live.com>

README.md

@@ -64,6 +64,17 @@ import { decodeTime } from "ulidx";
 decodeTime("01ARYZ6S41TSV4RRFFQ69G5FAV"); // 1469918176385
 ```
 
+### Validate ULID
+
+Import `isValid` to check if a string is a valid ULID:
+
+```typescript
+import { isValid } from "ulidx";
+
+isValid("01ARYZ6S41TSV4RRFFQ69G5FAV"); // true
+isValid("01ARYZ6S41TSV4RRFFQ69G5FA"); // false
+```
+
 ## Pseudo-Random Number Generation (PRNG)
 
 `ulidx` will attempt to locate a suitable cryptographically-secure random number generator in the environment where it's loaded. On NodeJS this will be `crypto.randomBytes` and in the browser it will be `crypto.getRandomValues`.