Issue with SqlChar in Convertible instance of SqlValue

[jeffhappily]

I'm having this issue where I have one table column with type tinyint but when I specify a Word8 type in my persistent models file, I get an error saying that

Failed to parse Haskell type `Word8`; expected integer from database, but received: PersistText \"\\STX\"

After some debugging, I found out that the library actually converts SqlChar to Persistent using this function called charChk where it converts \0 and \1 to boolean and other values to text

charChk :: Char -> PersistValue
charChk '\0' = PersistBool False
charChk '\1' = PersistBool True
charChk c    = PersistText $ T.singleton c

But as far as I can tell from hdbc-odbc, the SqlChar is actually being used to handle BindColBit and BindColTinyInt which are both meant to be used as an 8-bit number https://github.com/hdbc/hdbc-odbc/blob/06833d77799f16634d2038bcdc308c35d4752cdd/Database/HDBC/ODBC/Statement.hsc#L873-L880

I think a good fix here would be to convert the Char to PersistInt64 instead, as persistent handles nicely to convert PersistInt64 to either Word, Int or even Bool type.

I can open a PR if you'd like.

Related to #18

[gbwey9]

Thanks for taking a look at this.
The change you suggest makes sense and if you can open a PR I would appreciate it.