[sv-ec] Embedded covergroups - mantis #1239

Attached is a proposal for Mantis #1239.

The proposal 'clarifies' that a covergroup declared within a class is an
'embedded' covergroup. It makes the embedded covergroup TYPE anonymous.
The embedded covergroup declaration also implicitly creates a covergroup
variable (of the anonymous type). This replaces a number of special
rules regarding implicit variable declaration and limitations on the
usage of an 'embedded' covergroup type (the restriction are not needed
since the type is not visable).

There also was a special syntax (and note) that allows the variable name
to be omitted (implicit) in a variable declaration of an embedded
covergroup type. This optional syntax can be removed since variables of
embedded covergroups are now always implicitly declared - and cannot be
explicitly declared.

Finally, there is a syntax correction such that the call to 'new' can be
ommitted in the declaration of a covergroup variable for a non-embedded
covergroup. I.E. a regular covergroup variable can be declared without
instantiating (constructing) the covergroup in the variable declaration.

- Ray