`file` in the internal code and nondescriptive variable names

[chainsawriot]

It is inconvenient to have a variable called file all over the code, especially in the case of using the debugger, where the symbol file is also a base function name.

I don't think we can change the API of import(file) and export(x, file) for now. But I would suggest adding filename <- file or something like that immediate when entering the functions and then working on filename.

[chainsawriot]

Also,

type, file_type, compress, and sometimes ext are referring to a similar concept.

f, cfile, cfile2...

[chainsawriot]

f is also an unfortunate variable name, because in a debugger, it means "finish".