Fix some punctuation and grammar in background_loading.
Notes:
"**setup**" (a single [compound] word) is a _noun_ (a name for an object; a signifier [in Ferdinand de Saussure's semiology], a referrer, an identifier);
"**set up**" (two separate words) is an
_idiomatic_ (only makes sense when you take it as it is in its proper context)
_transitive_ (it takes a [direct] object [in a sentence -- grammar])
_phrasal_ (made up of more than one word)
_verb_ (something that expresses an action being done; a process).
Data on which functions are expected to operate:
"**argument(s)**" is the name for what a function takes in when it is being called/invoked/"conjured"/"summoned" [👿 occult language right there 😒];
"**parameter(s)**" is the name for that/those factor(s) that alter[s] what a function is designed to return when one is defining it 📜, usually introduced/"declared" in the function header.
"Low**-**level" is the correct spelling of the adjective.
* Minor Grammar and Naming Fix
Removed an extra "to" in comment.
Renamed var len to var length to avoid name conflict with len() and to make it more clear.
* Fix spelling error on my part
thanks @cbscribe
