get-path-function: expand default-directory by default

Because zoxide think `~` as an string instead of expanding it to home. This may
be done by shell normally, but this plugin uses poxis_spawn. Therefore, we
expand it here.
doc: fix the function description which were the pre version description.
readme: add tips for dired
readme: update readme
doc: fix style
doc: add more description for zoxide-open-with
add & remove: add a custom function to set how to get default path
readme: add doc for travel
travel: add a travel function
open-with: add non interactive to make callback can work in elisp
readme: update document
comment: fix typo
doc: take advice from `checkdoc`
fix typo error
fix parentheses match