Feature: compare results from two databases

**Description of the issue**

I am newbie to CodeQL.

My current process of creating database an extracting results follows:

```bash
#!/bin/bash
set -e

export CODEQL_SCAN_ID=$(date "+%Y%m%d-%H%M%S")

printf "CodeQL Scan ID: ${CODEQL_SCAN_ID}\n";

mkdir -p $HOME/.local/codeql/databases
cd $HOME/.local/codeql/databases
codeql database create \
--language="go" \
--source-root="${GOPATH}/src/github.com/greenpau/go-authcrunch" \
-- ./go-authcrunch-${CODEQL_SCAN_ID}

cd $HOME/.local/codeql
codeql database run-queries --ram=5922 --threads=2 --verbose \
--additional-packs . \
-- ./databases/go-authcrunch-${CODEQL_SCAN_ID} \
./queries-go/ql/src/codeql-suites/go-code-scanning.qls

cd $HOME/.local/codeql
mkdir -p ./results/go-authcrunch
codeql database interpret-results --format csv \
--output ./results/go-authcrunch/codeql_results_${CODEQL_SCAN_ID}.csv \
-- ./databases/go-authcrunch-${CODEQL_SCAN_ID}

printf "CodeQL Scan Results: "`pwd`"/results/go-authcrunch/codeql_results_${CODEQL_SCAN_ID}.csv\n"
```

I want to compare results from two versions of database for the same package, i.e. `go-authcrunch`.

As I am working through fixing issues, I want to be able to gauge whether my changes fix issues.