readtags: revise feature listing ptags (including an incompatible change)

[masatake]

• make -Q,--filter not work on ptags when -P,--with-pseudo-tags is specified together

  With this version, -Q,--filter option doesn't affect the pseudo tags listed with -P,--with-pseudo-tags option. -Q,--filter option specified wth -P,--with-pseudo-tags option affect only regular tags.

  To extract speicifed pseudo tags, use -Q,--filter option with -D,--list-pseudo action.

• make formatter work with -D,--list-pseudo-tags option

  An example extracting the value of !_TAG_PROC_CWD:

     $ ./readtags -t podman.tags -Q '(#/.*CWD.*/ $name)' -F '(list $input #t)' -D
     /home/yamato/var/ctags-github/
  

NOTE: the changes should not have a negative impact on Citre.