Add rseq syscall to strict sandbox mode

See merge request pwmt/zathura!51

Version 0.4.9

Error correction, changes and add-ons to the Spanish translation - es.po

See merge request !49

add syscall for strict sandbox

See merge request !50

Add option to display page number percent in statusbar

See merge request !48

Add source command

See merge request !47

Before, clicking on a link would always jump to the beginning of the
linked-to page, even when the link targets a specific point within the
page.

There are other expansions available, but I don't really think they make
sense, or why there are two of them for the same thing (`$FILE` and `%`
expand to the file name).

I added `$f` and `$p`, which expand to the document's path and current
page respectively, while keeping the other 2 just in case it breaks
someone's setup. I also documented them in both `zathura(1)` and
`zathurarc(5)`.

MuPDF supports xhtml files so let them by autocompleted too.

If bash_completion wasn't installed, _filedir wouldn't be defined which
led to all filename-based completions to error out. Specifically
autocompletion would fail when a filename was expected and when
bash_completion wasn't installed. Now we fall back to compgen -f if
_filedir fails. According to _filedir's comments, compgen doesn't
handle files with spaces well, but it is still better to complete most
files than none.

Version 0.4.8

Account for page padding on full scroll

Closes #52

See merge request pwmt/zathura!43