Ripped off blatantly from the suggestion made by @Crell.
Per @Crell, taking a stab at clarifying what the "tree of files" looks like, and what normalization needs to be done.
Per @Crell in the ML, this patch modifies the short-description lines of a number of methods that were wrapping to a second line, shortening them to fit on a single line. Additionally, a small number of signature changes were made for consistency: - `withStatus()` sets the default value of `$reasonPhrase` to a string. - `getReasonPhrase()` now only returns a string; if no value is present, an empty string is returned.
Slight change: if the header does not exist, instead of returning null, return an empty string. This is more consistent with `getHeader()` (which returns an empty array in the same situation), and with the `UriInterface` (where absence of a value returns an empty string).