_element: use compile-time string concatenation
_element: store the name of the element locally

It seems the ElementParser modifies itself, so it cannot be relied upon
for proper tag names.
_element: pass pointers to the Storage ctor
_element: no null fuses are passed
_element: use an OnlyOnce class instead of a bool

The bool was located on the stack and ruined later. Use a GC'd class
instead.
_element: don't pass Fuse objects as references

Same deal as the 'parsed' bool flags.
_element: fix argument name
_element: check fuses at the end of parsing

Throwing in the dtor ends up being about as fun as it is in C++ except
you throw the garbage collector into a frenzy.
elements: add defaults to attribute parsing
parser: use readText function

The InputStream reader seems to cause an mmap of a lot of memory for
some reason.
test_parse: write more informative output