[FEATURE] Support greaterThan and lessThan for range filters

A range filter cannot be easily used in Eel expressions since the
TypoScript parser does not allow double nested curly braces for
now. The two new query builder methods expose a high-level interface
for doing that.
[TASK] Update documentation
[FEATURE] Add greaterThanOrEqual and lessThanOrEqual operations
[TASK] Rename parameters in operations
Merge pull request #48 from networkteam/range-queries

[FEATURE] Support greaterThan and lessThan for range filters