change packages to bulleted list in readme

add Homebrew package to readme

fix typo in readme

bump version

document link regex option

update readme

create output dir if missing

refactor options.go

Re-arranged the ParseArgs function for improved readability.

implement regex link replacers

fix errors messages for link flags

add a changelog

remove conding standards from CONTRIBUTING

add contributing info

bump version

document output to stdout

Reading markdown from STDIN and writing to STDOUT was added a while ago,
but unfortunately the feature broke as I wasn't using it or testing it
myself. Recently, ~alterae <alterae@git.sr.ht> sent a patch fixing the
feature. This patch adds documentation to the README and man page.

Fix reading from standard input, writing to standard output

`options.ParseArgs` returns [] for opts if no files are specified, not
`nil`.  This commit changes the relevant logic to check for that,
allowing reading from standard input and writing to standard output.

upgrade dependencies

clean up readme and man page

update ConvertFiles documentation

improve comments in options package