Jess authored Jul 30, 2019 and Marge Bot committed Aug 06, 2019

Shake will be moving from its current implementation of ?== to one from
System.FilePattern. Support for `//` is being dropped, leaving only `*`
and `**` as special forms. This commit converts the existing file
patterns in Hadrian to the new format. It also removes all occurances
of <//> and changes the user-settings docs to remove references to //
and add **.

The conversion is as follows:

- //a ==> **/a

- a// ==> a/**

- a//b ==> a/**/b