Disambiguate single-item lists from parenthesized expressions.

[OliverHofkens]

The OData ABNF doesn't seem to distinguish between a single item list expression and a simple parenthesized literal (e.g. ('draft')). This currently breaks some expressions in this library.
Example failing case:
status in ('draft')

Ref: https://docs.oasis-open.org/odata/odata/v4.01/cs01/abnf/odata-abnf-construction-rules.txt
Grammar rules:

• parenExpr = OPEN BWS commonExpr BWS CLOSE
• listExpr = OPEN BWS commonExpr BWS *( COMMA BWS commonExpr BWS ) CLOSE

Currently, the workaround in odata-query is by forcing a listExpr through a trailing comma: ('draft',). It would be nicer if we could comply with the spec 100%.