Rename "Tool" to "Plugin"

[ChrisTimperley]

[xanderyzwich]

doo you just want the word changed in the README.md or is there something else needed? @ChrisTimperley

[ChrisTimperley]

@xanderyzwich this also requires changes to quite a few source code files. All references to Tool and tool, including partial references (e.g., ToolManager and __tools), need to be changed to Plugin and plugin.

Here's a (possibly incomplete) list of files that need to be changed:

• https://github.com/squaresLab/BugZoo/blob/master/bugzoo/core/tool.py
• https://github.com/squaresLab/BugZoo/blob/master/bugzoo/mgr/tool.py
• https://github.com/squaresLab/BugZoo/blob/master/bugzoo/manager.py
• https://github.com/squaresLab/BugZoo/blob/master/bugzoo/cli/controllers/tool.py
• https://github.com/squaresLab/BugZoo/blob/master/bugzoo/cli/app.py

It might be possible to use sed and grep to speedup the process.