Detect direct queries to COPY FROM
Initial COPY FROM support!

cc #51
Don't flush more than needed when copying
Correctly handle bad column counts in copy
Remove Binary/Text choice from ToSql

Text format doesn't work with our COPY implementation, and FromSql is
already binary only.
Add prepare_copy_in to transaction
Add some prepare_copy_in docs
Remove some unused methods
More docs + return copy count from execute
Add column_types to copy in statement
Remove failure from PostgresDbError::new

Closes #43
Don't fuse row iterator
Improve error handling in COPY
Use new slice syntax
Remove weird continue
Handle COPY IN in batch_execute
Clean up example a bit
Doc rephrase
Switch to servo's rust-url
Attempt at supporting date type