upgrade to 4.0.0 can no longer hash strings

[gabadie]

I just upgraded to 4.0.0 and immediatly got a test failure on 4.14.6 and 4.14.6t:

repro:

import xxhash
x = xxhash.xxh32()
x.update('hi')
*** TypeError: Strings must be encoded before hashing

Yet your 4.0.0 releases notes does not mention this breaking change about string encoding (https://github.com/ifduyue/python-xxhash/releases?page=1), and I can't find deprecation warning in previous releases notes >= 3.0.0.

Seams this change is from this commit: ff51b84

Many thanks!

[ifduyue]

I'll add it to changelog

[ifduyue]

80d42d2