encode all characters as required by rfc2231 #1

[brychcy]

fix for #1

[pabs3]

The patch looks good, but please adjust the commit message to look like this:

Encode all the characters that are required by RFC 2231 and RFC 5987

Parentheses and other characters were not being encoded.

Fixes: https://github.com/pst-format/libpst/issues/1

-- bye, pabs

https://bonedaddy.net/pabs3/

[pabs3]

I've rebased and merged the patch, thanks for your contributions.