Add `vessel install --force`

[rvanasa]

Resolves #55 by adding an optional --force / -f flag to vessel install.

Since this feature requires behavior equivalent to rm -rf, this PR also fixes a potentially major vulnerability in the form of using unsanitized package names or versions containing .., /, or ~, making it possible to modify (or delete) any directory on a user's machine. I fixed this by adding basic package name/version validation with the following rules:

• Package name/version must match the following regex: [A-Za-z0-9.-_]+ (i.e. the Portable Filename Character Set)
• Package name/version cannot consist entirely of the . character
• Package name/version cannot start with a - character

This validation could break backwards-compatibility with some unusually-named packages, but this seems to be worth it for security reasons.

[kentosugama]

Curious about your reasoning for using option 1 instead of option 2 from #55

[rvanasa]

Adding a flag to the existing install command seems like an elegant solution, especially since this is already a well-established feature in NPM and Cargo.

We could also add something like a release property in the future if this would be useful as well.

[rvanasa]

Would someone mind merging this while @kentosugama and I are waiting to get review permissions for this repository? Thanks!