Added HOARD_CONFIG env variable to specify config file

[seivan]

HOARD_CONFIG can point to a file path or a directory path where the file name would default to config.yml

export HOARD_CONFIG="~/.zsh/config/plugins/hoard_config.yml"

• Added shellexpand dependency.
• Expand tilde and variables for trove_path when reading config.trove_path
• Removed duplicate construction for HoardConfig.
• Added tests for reading env variable and making sure files are there.
• Split up reading path and creating files at paths.

Fixes: #346

[Hyde46]

Thanks a lot for the contribution!
Ill take a closer look and review this as soon as possible

[Hyde46]

Could you add this functionality to the Readme?
otherwise im happy to merge

[seivan]

@Hyde46 Done.