fix: properly parse non-url encoded file specs

[wraithgar]

Properly creates file package args that contain characters that need to be url encoded.

There is also a refactor/cleanup in here

• Removed the magic windows global for testing, fixing the tests to mock process.platform instead.
• Moved inline regexes up to where the others are defined
• Renamed a few variables to be more correct (i.e. isFilename to isFileType)
• Refactored Result to be a proper Class instead of a function w/ prototypes

Closes: #193

[wraithgar]

There still appears to be some incorrect behavior here, that was here even before this PR. saveSpec is a file: url but it is not url encoded. Most things this will generate won't cause decodeURI to throw:

> require('.')('/path/br[acket')
Result {
  type: 'directory',
  registry: undefined,
  where: '/Users/wraithgar/Development/npm/npm-package-arg/branches/gar_path-url-encoding',
  raw: '/path/br[acket',
  rawSpec: '/path/br[acket',
  saveSpec: 'file:/path/br[acket',
  fetchSpec: '/path/br[acket',
  gitRange: undefined,
  gitCommittish: undefined,
  gitSubdir: undefined,
  hosted: undefined
}
> decodeURI('file:/path/br[acket')
'file:/path/br[acket'

but some new characters that this now allows (like %) will:

> require('.')('/path/per%cent')
Result {
  type: 'directory',
  registry: undefined,
  where: '/Users/wraithgar/Development/npm/npm-package-arg/branches/gar_path-url-encoding',
  raw: '/path/per%cent',
  rawSpec: '/path/per%cent',
  saveSpec: 'file:/path/per%cent',
  fetchSpec: '/path/per%cent',
  gitRange: undefined,
  gitCommittish: undefined,
  gitSubdir: undefined,
  hosted: undefined
}
> decodeURI('file:/path/per%cent')
Uncaught URIError: URI malformed

I chose not to encode saveSpec in this PR because it's likely a breaking change. Consumers should always be decoding that, but they may not be currently.

[wraithgar]

Still some \ shenanigans to work out, evidently. The saveSpec normalization in the tests is likely hiding potential bugs.