This function returns the first non-NULL argument, or NULL if all are NULL.
Argument count is unlimited.
Includes a test in testdata.ql.
Fixes #211.

Implement the SQL standard COALESCE function.

Closes #211

See merge request !209

This allows key words and other formerly not allowed identifiers to be used.
Guillemets were chosen because all other string escapes were already used
in the grammar of QL.
Also implemented some unit tests.
Fixes issue #210

Implement delimited identifiers between guillemets.

Closes #210

See merge request !207

Fix failing test. Newlines are not alowed in identifiers between guillemets.

See merge request !212

Fixes #219.

Fixes #220.

ql: replace string(int) conversions w/ string(rune(int))

Closes #220

See merge request !217

Added new ql logos

See merge request !219