ability to parse extra parameters to mysql jdbc

[mprokopov]

Allows specify extra parameters for mysql jdbc driver in map under key :extra

example:

(def db-params (mysql {:host "localhost"
                   :db "itservice"
                   :user "root"
                   :extra {:useLegacyDatetimeCode false
                           :serverTimezone "UTC"
                           :useSSL false}}))

this appends "?useLegacyDatetimeCode&serverTimezone=UTC&useSSL=false" to subname

[jiacai2050]

Is there anyone looking into this ?

[venantius]

In general this approach seems fine, but it needs tests before we'll be able to consider merging it.

[venantius]

Don't change the project name.

[zjjfly]

though we can specify extra parameters in :db,this pr offers much better clearity