jsx-to-htm: leading underscore = reference tag

[developit]

In JSX, a leading underscore in tag names denotes a reference tag (Component):

var x = <_Foo />
// should output:
var x = html`<${_Foo} />`

[developit]

Updated to allow both $ and _ leading characters to indicate referential tag names, as well as the existence of . anywhere in a tag name:

Tag Name	Type
div	string
div_	string
div$	string
d_v	string
d$v	string
F	reference
Fragment	reference
React.Fragment	reference
react.fragment	reference
$div	reference
_div	reference

(Babel seems to parse tag names matching /(^[A-Z_$]|[A-z_$]\..)/ into references. repl example)

[jviide]

Looks good to me 👍