Picotool incorrectly flags parenthesized expressions as assertionerrors
The error message for all of these cases is always AssertionError, thrown at `self._tokens[self._pos].matches(lexer.TokSymbol(keyword))` in `lua.py`.

**Parenthesized functions**
AssertionError (expected `)` got `(`):

```lua
dbg=(function()
end)()
```

Correctly parsed:
```lua
dbg=function()
end
dbg = dbg()
```

**Parenthesized tables**
AssertionError (expected `)` got `:`):
(note: tables have __sub methods defined in metatables)

```lua
somefunction({(table1 - table2):unpack()}))
```

Correctly parsed:
```lua
local temp = (self.pos - self.anchor)
somefunction({temp:unpack()}))
```