add support for client_encoding option with pgsql (fix #16)

[haruspeks]

What kind of change does this PR introduce? (pls check at least one)

• [x] Bugfix
• [ ] Feature
• [ ] Code style update
• [ ] Refactor
• [ ] Build-related changes
• [ ] Other, please describe below

Description

When connecting to a pgsql instance, option charset is not supported. The correct option to be set in the dsn should be client_encoding, see docs.

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

Related Issue

See issue #16 .

[mychidarko]

Thanks for the fix