reconhub/aweek: aweek version 1.0.0

This version is presented of aweek is presented as a more mature and stable version of aweek:

• combining objects is more predictable
• weeks/dates can be created from vectors with heterogeneous week_starts
• documentation is improved
• data frames can be created

• change_week_start() allows the user to change the week_start attribute of an aweek object, adjusting the weeks to match the new attribute accordingly.
• get_aweek() can generate aweek objects from a vector of week numbers. It has the ability to take into account different week start times.
• get_date() is similar to get_aweek(), but returns dates instead.
• as.aweek() allows users to create aweek object directly from characters with validation. It also allows for dates by passing to date2week().
• as.data.frame.aweek() is a new function that allows aweek objects to be directly incorporated into data frames.
• as.list.aweek() will now preserve the aweek structure in lists
• trunc.aweek() will truncate the day to the first day of the week.
• rep.aweek() allows repeating aweek characters.
• factor_aweek() allows the user to create aggregated aweek objects on the fly.

There are a couple of breaking changes coming to aweek that will improve stability by removing unclear coercion methods (see https://github.com/reconhub/aweek/issues/20).

• It is no longer possible to combine aweek objects if they do not share the same week_start attribute. This will result in an error informing the user to adjust the week_start attribute with the change_week_start() function.
• Factors will no longer coerce factors when combining aweek objects.
• Using date2week() with factor = TRUE and floor_day = FALSE now throws an error instead of a warning (as prophesized in #13).

• The vignette has been updated to include an explanation of the underlying week calculation from date.
• The aweek class documentation has been updated to detail the different elements of the object and the calculations.
• Package documentation package?aweek has been added for an introduction.

• conversions will now retain the names of the object.

• More checks that weekdays and weeks are within the correct bounds have been added.
• as.Date.aweek has been simplified to no longer rely on regex since the aweek class is standard.
• The internal get_wday() has been vastly simplified with improved speed.