EditorConfig parsing doesn't match spec

[ToddGrun]

1. Per spec, the key can contain non-prefix and non-suffix spaces. Roslyn doesn't appear to allow this.
2. Per spec, key and value are separated by '='. Roslyn appears to allow an ':' to also separate the key and value.

Both of these issues are in relation to the regex here.

Potential regex string

"^\s*([\w\.\-_]+(?:\s+[\w\.\-_]+)*)\s*=\s*(.*?)\s*$"