using keyword extension

[inky03]

allows the static extension using keyword to be used for any class; also an attempt to improve its behavior

• using the keyword will also import the class, as intended
• prioritizes checking if a function exists on the object before checking if it exists in an extension
• also adds a type check function to UsingEntry, helpful to enhance currently existing entries in allUsings and also to prevent the interpreter from failing if a function has a null return value (ex. using Lambda, <Iterable>.find returning null if it doesn't find a matching item)

i also updated the stringtools test asset to reflect some of these changes

[NeeEoo]

@crowplexus how do we change this to dev branch? Or is this synced with the latest version? Because my moved code we did isnt here

[NeeEoo]

Wait this is already dev branch

[NeeEoo]

Ohhh @crowplexus you forgot to push your local changes

[crowplexus]

Ohhh @crowplexus you forgot to push your local changes

I will push it soon

[NeeEoo]

I had it as a string to allow people make custom usings,

but please do wait until we push our local changes

[crowplexus]

updated master and dev branches