Note, configs and other files from ~/.elinks/ are not moved
to ~/.config/elinks/ automatically. You must do it yourself.
ELINKS_CONFDIR and HOME_ETC also are no longer supported.
Be more strict about the format accepted by the ELinks specific extension
to the -remote URL syntax. That is, commands must begin with a nonempty
sequence of ASCII alphabetic characters followed by optional whitespace and
an opening parenthesis. Also, document the syntax.
Fixes bug 830.
