Nonstandard operator priorities

[Cardillan]

The priority of operators, as currently defined, is somewhat unusual. In Mindcode, we have:

1. ternary operator ? :
2. assignment =, /=, **=, -=, +=, *=
3. exponentiation **
4. unary negation !, not (see also #72 for this)
5. multiplication *, /, \, %
6. addition +, -
7. shift <<, >>
8. inequality comparison <, <=, >, >=
9. equality comparison ==, !=, ===
10. bitwise operation &, |, ^
11. boolean and and, &&
12. boolean or or, ||
13. unary minus - (this isn't working at the moment, but let's ignore it)

Some of this can be a bit surprising. Compared to other languages, both the ternary operator and assignments are way too high. The most obvious example I stumbled upon is a = b > c ? 0 : 1, which gets compiled to a wee bit unusual a = b > (c ? 0 : 1). I don't use assignments as expressions much, but it would in all probability behave in similarly unexpected ways.

I propose changing the order to a more common one (I tried to do it according to Ruby):

1. unary negation !, not, ~
2. exponentiation **
3. unary minus - (I'll try to make it work while at it)
4. multiplication *, /, \, %
5. addition +, -
6. shift <<, >>
7. bitwise and &
8. bitwise or/xor |, ^ (this would mean splitting the binop_bitwise_op category in two, all others are just reordering of existing terms)
9. inequality comparison <, <=, >, >=
10. equality comparison ==, !=, ===
11. boolean and and, &&
12. boolean or or, ||
13. ternary operator ? :
14. assignment =, /=, **=, -=, +=, *=

@francois, as this is again a code-breaking change (hopefully last from me for some while), would you be ok with me implementing this?

[François Beausoleil]

LGTM, go ahead. I would also appreciate if you changed the README / HTML to document the Mindcode operator precedence rules. I am not experimented enough and got my priorities wrong.

[Cardillan]

I will update the syntax document as well. I thought about expanding it a bit anyway.