Deprecation of has_keys

[jjg-123]

Currently there is the function has_keys(arg., list.) which will take the list of indices the right hand side and return a list with boolean values for each element. E.g.

   has_keys({'a':0,'c':1}, ['a','b','c'])
[true, false, true]

This is ok, but has two major shortcomings.

1. Most functions now are left conformable, so the shape of the result is the same as the left argument. This makes chaining functions a snap f(g(h(larg., rarg.),...)
2. Having a list of elements means having to explicitly loop over everything rather than use the implicit looping that QDL excels at.

Therefore, a new function has_key(l_arg., r_arg.) (note there is no final s) has been introduced that works like it should., E.g.

   ccc.:={'a':0,'b':1,'c':2};
   ddd.:={'a':[0,1,2,3,4], 'b':-1, 'c':2, 'd':3, 'e':4};
   has_key(ccc.,ddd.)
{a:true, b:true, c:true}
   has_key(ddd., ccc.)
{a:true, b:true, c:true, d:false, e:false}

In other words, has_key gives a map of keys so we can just compare them and do things like select elements without looping:

   mask(has_key(ccc., ddd.), ccc.)
{a:0, b:1, c:2}

Takes the elements in ccc. that are in ddd. (Using has_keys would require taking the result, then creating a stem that conforms to the arguments of mask, which is just annoying, or just writing out loops that do what mask does, which defeats the purpose of having a function for mask.)

Also, this affords a scalarized version, that checks if a single index is in a stem:

has_key(i, r_arg.)

returns a boolean if i is an index in r_arg. E.g.

   has_key('a', ddd.)
true

**Therefore, the proposal is to deprecate has_keys and eventually remove it from the system, since it just is not that useful, hence mostly unused. **