EWKB adaptor does not support SRID on write

[saintsjd]

Looks like the read function for EWKB adaptor supports SRID. The write function does not.

Support for SRID on write is needed in order to save records to postgis in EWKB format when the SRID is set on a geometry column.

[dark-panda]

I've implemented a fix for this and have opened up a PR for it at #119.