Augment properties decl syntax to support setting an initial value

[hopscc]

Properties declaration recently augmented to implicitly declare ( or not require an already declared) backing variable.
Extend this slightly to also support setting an initial value to this implicit backing variable
i.e.

pro val from var as int = 99
#equivalent to 

var _val as int = 99
pro val from var

see also discussion in
 Declaring backing vars for properties on the same line

[Chuck]

So it's:

pro val from var = 99

# general form:
pro|get|set <name> from var = <expr>

[hopscc]

patch + some refactoring and cleanup
tests and relnote

[Chuck]

I am working on this. Have a conflict to resolve from some work I did on type declaration clauses.

[Chuck]

Patch applied.

I found an oddity in the test cases that a "pro x from var as FOO" could redeclare the type of a previous "var _x" to something different. That's a bug, not a feature.