assert variable, identifier and function names to be plain strings
added missing import
fixed constant container name
callable name factories, e.g. `F('foo')` equivalent to `F.foo`
allows creating instances when you have the name in another var, i.e. `F(var)` shorthand for `getattr(F, var)`
shorthand `L` for turning literals into expressions
example usage: `SELECT(L('constant string').AS('alias'))`