Improve Windows Support

Currently, the package does not support Windows completely. Major reason for that is UTF-8 is not extensively supported by cmd, powershell etc.

[marton-schmalzl]

The ability to provide fallbacks would be nice, something like this:

{
    'interval': 100,
    'frames': ['★', '☆'],
    'fallback_frames': [ '*', ' '],
}

[t-makaro]

When using windows terminal, it sets the environment variable “WT_SESSION” this can be used to ensure proper compatibility with windows terminal and non-windows terminal terminals.