Fix server error handling

Fixes libattachsql/libattachsql#5
Merge pull request #17 from LinuxJedi/server_errors

Fix server error handling
Now with multi-statement/result support!

Fixes libattachsql/libattachsql#6
Document next result function
Merge pull request #18 from LinuxJedi/multi_statement

Multi statement
Hopefully fix clang Travis failure

Can't reproduce it yet