The vast majority of jumps will end up within the current opened
file/buffer, simply because usually users do more movement inside a
buffer rather than across buffers.

There is even a special case when evil-jumps-cross-buffers is set to
nil, which causes jumps never ever switch buffers.

So, let's do a small optimization, and not try to call find-file or
switch-to-buffer if we know it is unnecessary.

As a side-effect, this should also help to users to stumble less upon
https://github.com/emacs-evil/evil/issues/1504 bug (it has its own
upstream fix, but until that landed, this small optimization is known to
help as well).

All commands that change the current buffer are jump commands. This
was previously implemented using advices, but this did not catch all
all applicable commands: find-file, for example, was ignored.

Instead, use the post-command-hook to check if a command changed the
buffer.

Correctly handle the case of POS being a marker located in a buffer
other than the current one.

evil--jumps-message did not evaluate its args parameter.