adding parameter options for gc_event_ls()

[paddytobias]

not sure if this is written the best way but it works (e.g., if you use gc_event_ls(params = "maxResults=1000")). There will need to be checks placed on what parameters can be used and in what ways with this function. The current version doesn't do this

[yogat3ch]

This commit completes the features of the function outlined in the manual

An arbitrary number of optional query parameters may be supplied via .... A list of optional query parameters can be found in Events: List.

Notable parameters include:

q – Free text search terms to find in any field.

singleEvents – Logical indicating whether to expand recurring events into instances and only return single one-off events.

timeMax – Exclusive upper bound of the start time filter (formatted as an RFC3339 timestamp).

timeMin – Inclusive lower bound of the end time filter (formatted as an RFC3339 timestamp).

The currently deployed function does not provide this functionality despite the manual saying it does.
@benjcunningham Please commit this change as it adds the missing functionality.