fix #179
removed .Error() in logger, removed mutex to set logger
add CHANGELOG entry
Merge pull request #182 from arnehormann/configurable-logger

add a configurable logger
NUL-terminate old password scramble
DSN: check for separating slash

Fixes #186
Merge pull request #187 from go-sql-driver/dsn_trailingslash

DSN: check for separating slash
Merge pull request #188 from go-sql-driver/oldPasswords_fix

NUL-terminate old password scramble