Drop dependency on f.el

Use Emacs' built-in file functions instead
Update eslint testcase
Disable go-errcheck in test case

Fixes warnings about typecheck failure
Add FSF copyright

Since we copy some code from Emacs for backwards compatibility, we must
preserve the copyright notice of the FSF
Unquote argument to bound-and-true-p

This function takes an unquoted symbol.
Remove redundant require
Drop dependency on s.el
Reduce excessive use of threading macros
Use standard dolist/mapc in place of -each/--each
Replace -map with standard mapcar
Get rid of all anaphoric macros

Make our code more idiomatic Emacs Lisp by using higher order functions,
i.e. lambdas or apply-partially instead
Simplify expression
Avoid construction of an intermediate list
Use macroexp-progn instead of raw progn forms
Update Texinfo manual
Remove leftover require.
It's subr-x, not subrx.
Merge pull request #430 from Fanael/master

Remove leftover require.
Merge pull request #431 from Fanael/subr-x

It's subr-x, not subrx.
Use pcase-dolist to simplify iterations