Merge upstream changes up to commit d3456309

[illia-li]

Original commit list:
1. apache@3a475c7
Message:

CASSGO-44: keep nil slices in MapScan
Previously if you read a NULL column as a varchar using MapScan it
would store the value []byte{} in the map rather than []byte() which
made it impossible to know if the value was NULL or not.

Patch by James Hartig; reviewed by João Reis for CASSGO-44

Status: APPLIED

2. apache@c63468d
Message:

CASSGO-42: don't panic if no applied column is returned
I also added checks against MapScan failing which could also trigger this bug.

Several integration tests were added to validate various edge cases.

Patch by James Hartig; reviewed by João Reis for CASSGO-42

Status: APPLIED

3. apache@91cbf12
Message:

skip metadata only if prepared result included metadata
If the prepare result doesn't include metadata we shouldn't skip metadata
when executing the query. Fixes CASSGO-40.

Patch by James Hartig; reviewed by João Reis for CASSGO-40

Status: APPLIED

4. apache@16366d4
Message:

Improve error messages for marshalling
Enhancement for marshal/unmarshal error messages.
Errors were updated by the supported types list.

patch by Oleksandr Luzhniy; reviewed by João Reis, James Hartig, Bohdan Siryk, for [CASSGO-38](https://issues.apache.org/jira/browse/CASSGO-38)

Status: APPLIED

5. apache@d345630
Message:

CASSGO-2 Marshal big int returns variable length slice.
The marshalBigInt return 8 bytes slice in all cases except for big.Int,
which returns a variable length slice, but should be 8 bytes slice as well.

patch by Mykyta Oleksiienko; reviewed by João Reis, James Harting for CASSGO-2

Status: APPLIED