SQL Server TVP; Various Fixes

Many thanks to the community for this release:

• Thanks to @v-makouz and @v-chojas , support for SQL Server Table-Valued Paramaters has arrived. See test_tvp in the SQL Server unit tests.
• Support for IBM DB/2 DECFLOAT type (#472) by @C-DY
• Better SQL Server and FreeTDS tests with known driver issues (#469) by @gordthompson.
• Fix "function sequence error" with fast executemany (#450) by @v-makouz.