dint 2.0.0.9000

added ggplot2 scales for dint data types
added predicates to check whether dates correspond to the boundaries of years or quarters (is_quarter_bounds(), is_year_bounds(), is_first_of_quarter(), etc…)
export methods for unique and summary that were introduced in the last version but mistakenly not exported
One can now subtract two date_xx of the same subclass from each other (the result is an integer)
added as_yearmon() and as_yearqtr() for converting to zoo S3 classes
Removed functions that were deprecated with dint 2.0.0
added Sys.date_yq(), Sys.date_ym() and Sys.date_yw() to get the current quarter, month or isoweek.
lots of small fixes

dint 2.0.0

breaking: formatting date_xx objects now uses placeholders similar to base::strptime() (e.g %Y, %m, %q, etc…) instead of presets. The new implementation is also noticeably faster than the old.
breaking: all first_day_of_*() and format_date_y*() functions now have shorter names: first_of_*() and format_y*(). The original names will still work until the next release but give a deprecation warning.
Added support for c(), min(), max(), range()
You can now directly supply a numeric year to first_of_year() and last_of_year() (e.g. first_of_year(2018))
added date_yw for storing isoweeks and modified existing functions to accommodate for them.
added [ method for date_xx objects that preserves class attribute when subsetting
%y+% / %y-% can add/subtract years from date_xx objects
added the predicates, is_first_of_quarter(), is_last_of_quarter(), and is_quarter_bounds().
seq() methods now support a by argument