[WIP] add command to convert inputs to new format

[rpetit3]

yo! This is totally a work in progress and there will be things to work through, but this was what I was thinking. Figured best to get it here so you could suggest/comment.

Here's an example using the Travis CI yaml from Snippy

wget -O snippy-travis.yml https://github.com/tseemann/snippy/raw/master/.travis.yml
write-the convert snippy-travis.yml --input-format "Travis CI YAML" --output-format "Github Actions YAML"
Converted Output:
```plaintext
name: CI

on: [push]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v2
    - name: Set up environment
      run: |
        export PATH=$PWD/bin:$PWD/binaries/noarch:$PWD/binaries/linux:$PATH
        apt-get update
        apt-get install -y libstdc++6 liblzma5 libbz2-1.0 bioperl
    - name: Check libraries
      run: |
        ! (ldd $PWD/binaries/linux/freebayes | grep 'not found')
        ! (ldd $PWD/binaries/linux/vcfuniq   | grep 'not found')
        ! (ldd $PWD/binaries/linux/samtools  | grep 'not found')
        ! (ldd $PWD/binaries/linux/bcftools  | grep 'not found')
    - name: Check versions
      run: |
        snippy --version
        snippy --check
        snippy-core --version
        snippy-core --check
    - name: Test
      run: make -C test

Would need to do some testing on my end, but first glance it looks like a functional GitHub Action yaml.