[BUG] Handle local cargo installs better

[jayvdb]

Describe the bug
Installing a path of . shouldnt be registered as '.'.

To Reproduce

cargo install --path .
  Installing emplace v1.3.1-alpha.0 (/Users/john.vandenberg/osx/emplace)
    Updating crates.io index
   Compiling libc v0.2.89
   Compiling proc-macro2 v1.0.24
....
    Replaced package `emplace v1.3.0` with `emplace v1.3.1-alpha.0 (/Users/john.vandenberg/osx/emplace)` (executable `emplace`)
Opening Emplace repo: "/Users/john.vandenberg/Library/Application Support/emplace".
Mirror this command?
- . (Cargo Rust)
[y/n]

Expected behavior
Dont try to register '.' as an installable, or expand . to be a complete path, and even better would be to determine the git repo and hash to make it reproducible.

Desktop (please complete the following information):

• OS: mac
• Shell: zsh

Machine information

Software version

emplace 1.3.1-alpha.0

Operating system

Darwin 20.3.0

Environment variables

SHELL=/usr/local/bin/zsh
EMPLACE_CONFIG='/Users/john.vandenberg/Library/Application Support/emplace.toml'

Git version

> git --version
git version 2.31.0

Compile time information

• Profile: release
• Target triple: x86_64-apple-darwin
• Family: unix
• OS: macos
• Architecture: x86_64
• Pointer width: 64
• Endian: little
• CPU features: fxsr,sse,sse2,sse3,ssse3
• Host: x86_64-apple-darwin

[jayvdb]

A more vague pip example found via history import:

[ ] requirements.txt (Python Pip)

There, the name requirements.txt could actually be a valid PyPI name, so simply doing heuristics on package name wouldnt suffice, however it would be a great first implementation.

[tversteeg]

I've added a heuristic that ignores packages that start with a special character. The requirements.txt for Python is a bit of a different case, I think I'll need to have a blacklist for each package manager for that.