Themes

I suggest the following API:
```sh
# use the "poop" theme:
krasivo hello --theme poop
# or, shorter:
krasivo hello -t poop
```
We can also support user-defined themes and settings via a `~/.krasivorc` file or something. Example:
```yml
# ~/.krasivorc
default_theme: poodle
themes:
poodle: :poodle: :poop:
thoughtful_pray: :thinking_face: :pray::skin-tone-6:
```
```sh
# use "poodle" theme by default:
krasivo "no thanks"
# still able to use krasivo normally:
krasivo hey :no_good: :dog2:
```

This feature isn't that good without a selection of default themes that would be bundled with the package. And for that, I need help. Please offer your theme ideas here, if you have any.