Consider adding singleton instances

[sandrock]

As SekvapLanguage does not maintain a state related to the data it processes, we can create a singleton instance. This would avoid declaring/creating too many instances in our apps.

These two static instances would help a lot:

SekvapLanguage.Default = new SekvapLanguage();
SekvapLanguage.TrimAllWhispaces = new SekvapLanguage()
{
    TrimKeyStart = true, TrimKeyEnd = true,
    TrimValueStart = true, TrimValueEnd = true,
};