Investigate better pagination options for Greg\EventQuery

[sdunham]

We're currently setting 'posts_per_page' => -1 in Greg\EventQuery::params() to ensure that all applicable events are returned based on the current query. Without this, the query would be limited based on the WP posts_per_page setting. But there are probably better and more flexible approaches for this.

See #14 for more context on why this change was implemented in the first place and some potential suggestions for future improvements.