and move eslint config to package.json

Addresses #224 and properly parses all C++ numbers.

This change allows operators (not just fields/member functions) as dependent
template expressions.

```cpp
auto x = y.template operator()<int>();
```

This syntax is used e.g. to call C++20 lambda expressions with a template head
where the template arguments are not function arguments and therefore cannot be
deduced.

```cpp
[]<typename> () {}.template operator()<int>();
```

This change allows commas inside subscripts.

```cpp
auto x = a[1, 2, 3];
```

From C++23, array subscripts work like arguments to `operator[]` as an n-ary
function.

Before C++23, `operator[]` must be a unary function, but before C++20, it's
possible to use the comma operator inside subscript expressions - and this is
done in libraries that use expression templates to achieve multidimensional
array syntax.

Use of the comma operator in subscript expressions was deprecated in C++20 to
make way for the C++23 change to n-ary `operator[]`.

breaking change: namespace_definition_name has been renamed to
nested_namespace_specifier and the nesting has been reversed to match
the way normal scope resolution works elsewhere.

identifiers that are part of a namespace_definition are now
namespace_identifier, which matches the identifier node type used in
scope resolution for qualified types.

namespace alias definitions use the new nested_namespace_specifier so
all identifiers are namespace_identifier nodes.

support for top-level "inline" namespace declarations (which are valid
if they are nested in another namespace body).

Fixes #193

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

Fixes #184