breaking changes:
- access_specifier is now a named node in base class clauses
- virtual_function_specifier node has been renamed to virtual

Support for function-try-block implemented in #168/#169 was not correct:
member initializer list in constructor must appear between `try` and the
opening curly brace. Also some cases where try block is allowed were not
implemented.

Following changes are included:

* fix initializer list handling in try block in constructors,
* disallow initializer list in =default/=delete constructors,
* allow for try block in inline function definition,
* allow for try block in cast operator definition.

Fixes #168

!! Breaking change due to restructuring and renaming of scoped identifiers !!

Scoped identifier rules have been renamed to "qualified_x_identifier"
and all variants are aliased so they appear as simply
"qualified_identifier" in the syntax tree. This name better reflects the
c++ standard's language describing this concept.

Qualified identifier rules are now always the "parent" with a right
associative rule that lets them nest indefinitely. Each rule terminates
with some kind of non-scope identifier.

This commit also adds support for the 'template' keyword where required
to disambiguate dependent template names. Field accessors (., ->) can be
followed by keyword template before a template method. The scope
resolution operator can be immediately followed by the 'template'
keyword to indicate the following dependent name with '<' is actually a
template and shouldn't be parsed as a binary operator. These keywords
are required for dependent names in these contexts.

Fixes #48

Fixes #17

Co-Authored-By: Thomas Johansen <thomasjo@gmail.com>