[bug report] Not all legal package names are legal eyeglass names

Nobody has claimed this yet.

If I name an eyeglass module `prefix.tool-name` or `prefix_tool-name` both of which are [legal package names](https://docs.npmjs.com/files/package.json) according to the NPM docs, eyeglass can't find my module.

e.g. this breaks
```
{
"name": "prefix.tool-name",
"version": "1.0.0",
"main": "stylesheets/_prefix.tool-name.scss",
"eyeglass": {
"needs": "^1.0.0",
"name": "prefix.tool-name",
"exports": "eyeglass-exports.js"
},
"keywords": [
"eyeglass-module",
"sass"
]
}
```

Changing the module name to `prefix-tool-name` causes the import to work fine.

i.e. this works:

```
{
"name": "prefix.tool-name",
"version": "1.0.0",
"main": "stylesheets/_prefix.tool-name.scss",
"eyeglass": {
"needs": "^1.0.0",
"name": "prefix-tool-name",
"exports": "eyeglass-exports.js"
},
"keywords": [
"eyeglass-module",
"sass"
]
}
```

There doesn't seem to be anything I can see in the docs about requirements for module names

Start with the package.json examples and reproduce the failing imports for prefix.tool-name and prefix_tool-name, comparing them with the working prefix-tool-name case. Trace eyeglass's module lookup using stylesheets/_prefix.tool-name.scss and eyeglass-exports.js; done means legal package names resolve consistently without requiring a renamed eyeglass name.

Written by the indexing model from the issue text.