Added SQLSERVER_STRINGS macro to work around fix for #70.
 * In SQL Server, SQL_WLONGVARCHAR corresponds to the deprecated ntext data type. nvarchar(max) is the preferred option.
 * To use nvarchar(max), you use SQL_WVARCHAR with a column size of SQL_SS_LENGTH_UNLIMITED (zero). This may or may not probably cause other drivers to send an empty string (?), which is why I've added this as a #define.

This isn't the best solution, since it doesn't support connecting using different drivers at the same time, but I don't know what a better solution would be.
Formatting
Merge branch 'sqlserver-strings' of https://github.com/lee-houghton/node-odbc into v0.6
Remove SQLSERVER_STRINGS define check and always use size 0 for varchars; breaks FreeTDS
Rename Parameter stuct members to match the parameter names of the SQLBindParameter function

I was always try to map in my head what went to what, so it was simpler to
just rename the struct members to what they actually are instead of the
somewhat cryptic names