Update explainer to introduce `~()` for partial application

[rbuckton]

This make the following changes to the proposal:

• Adds a ~ prefix to denote a partially applied argument list (i.e., f~(?, x)).
• Adds ?0 ordinal placeholders.
• Adds a ... "rest of the arguments" placeholder.
• Allows use of partial application with new.
• Removes partial application with template literals and tagged templates.
• Removes (or rather, comments out for the time being) references to the pipeline operator.

Fixes #48 Fixes #43 Fixes #5

[jonatjano]

I see no mention of what happens when you use the same ordinal placeholder multiple times

const surround = String~(?1, ?0, ?1);
surround("text", "__"); // "__text__" ?

The explainer doesn't say if it is forbidden or if the argument is applied twice as expected (Or did I overlook it ?)

[tabatkins]

You overlooked it - check line 115.

[rbuckton]

const surround = String~(?1, ?0, ?1);
surround("text", "__"); // "__text__" ?

Although, the String constructor doesn't work that way. I think you would want "".concat(?1, ?0, ?1) instead.

[rbuckton]

Merging, thanks for the feedback!