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Change API to provide 4 functions:

• New - generates new ID
• Must - generates new ID and panics on error
• Generate - generates new ID with custom alphabet and length
• MustGenerate - generates new ID with custom alphabet and length and panics on error

Furthermore some tests were changed/adjusted/added which revealed a bug with custom alphabet containing non-ascii characters.

Add MustID and MustGenerate functions. Similar to ID and Generate but panic on error.

• Generate valid id for any alphabet (support for non-ascii alphabets)
• Add more complex examples

• Add ID(length) function, shorthand for Nanoid().
• Add checks for parameters of Nanoid() function.

• Update golang to 1.14

• A release with all that's needed same as implementations in other languages.