Use right store dir to ensure `pass-view-mode` activate properly

Support extraction of fields other than password

Allow users to retrieve any secret field stored in the file.
The new command, `pass-copy-field' receives the wanted field as input,
and returns its secret value for the entry at point.

For convenience, the two new commands `pass-copy-username' and
`pass-copy-url' handle the common case for an user login (Issue #29).

The new command `pass-browse-url' directs the default browser to the
stored url at the entry at point.

Replace Emacs dependency from v24.3 to v25, as password-store.el.
Bump version to v1.9.

* pass.el (pass--copy-field): Use `password-store-parse-entry'.
(pass-username-field): New option
(pass-copy-username): New command.  Bind it to 'b'.
(pass-copy-url): New command.  Bind it to 'u'.
(pass-browse-url): New command.  Bind it to 'U'.
(pass-copy-field): New command.  Bind it to 'f'.

* README.md: Document the new keybindings.

Add feature to jump between entries

This test fails for Emacs 24; actually, password-store
requires Emacs-25 (it uses `make-process').
* test/pass-tests.el (pass-goto-entry-tests): Delete it.

* pass.el (pass--drop-dir-headers): Delete it.
(pass--entries): Delete it.  Use password-store-list, instead.
Update all callers.

Add a command `pass-goto-entry' for moving to any
entry in the pass buffer.
Update copyright notices.
* pass.el (pass--drop-dir-headers, pass--entries)
(pass--target-entry-pos): New internal functions.
(pass-goto-entry): New command; bind it to 'j'.
(pass-show-keybindings): Show it in the header.
(pass--display-keybinding): Update formatting to give enough space
for the new command description.

* test/pass-tests.el (pass-goto-entry-tests): Add test.

* README.md: Document the new keybinding.

Do not create entries for Emacs backup files

Emacs backup files might contain an out-of-date password, thus
these entries must be ignored.
* pass.el (pass--tree): Ignore Emacs backup files (Fix issue #31).

* pass.el (pass-view-mode): Do not fontify strings or comments.

Display confirmation message after copying password to the kill ring

See merge request nico/pass!15

Derive pass-mode from fundamental-mode

With this, imenu will display "foo/bar" for a "foo/bar.gpg" entry
instead of just "bar". This is important as there might be multiple
bar.gpg files in different directories.

OTP Support

Only use the major mode for gnupg files

* Allow colons in keywords.
* Disallow spaces in keywords.

When called with a prefix argument, `pass-insert` visit the new entry.

Fix #17

Properly ignore .git directories

Do not try to find entries when on a directory.

Fix invalid function definition

* pass.el (pass--tree): Call delq at the right place.

Docstring and first form of BODY were swapped.

Fix #11

Amend docstring for pass-copy