More secure charsets

All of the old charsets for gouid.String() have been removed, since their lengths were not factors of 256. In their place, two charsets have been added: gouid.Secure32Char and gouid.Secure64Char. These will ensure an even distribution of characters and will be cryptographically secure.

v0.5.2: Merge pull request #5 from twharmon/docs

Fix doc typo

v0.5.1: Merge pull request #4 from twharmon/codecov

Remove codecov token

v0.5.0: Merge pull request #2 from twharmon/simple-string

Simplify String() method

v0.4.0: Merge pull request #1 from twharmon/string-doc

Fix String documentation

v0.3.0

Reformat benchmarks in readme

v0.2.1

Implement Stringer interface

v0.2.0

Add tests

v0.1.0

Add some documentation

Hex encoding for json

v0.0.3

Use hex encoding with json