Bug: Boolean filtering by tags does not work @a | @b
Filtering by @a | @b should give all tasks tagged with "a" OR "b", showing all that have one or the other or both.
Currently this only shows the first tag and ignores the rest.
Also, a new @a & @b filter should exist; this one returning "a" AND "b" showing all tasks that have BOTH tags in them.
Of course this should be extended for multiple tags @a | @b | @c |@n .... @a & @b & @c &@n ....
A refined use should include parenthesis so that precedence of operators can be defined, such as (@a | @b) & @c