lambcmd should set `<title>` of HTML document from `\title` by default

[edwintorok]

I get Lambdoc document, and apparently there is an undocumented --title command that I could use (as used by the Makefile that builds the lambtex manual). Please document --title in lambcmd's --help, and set it by default to \title from the document.

[darioteixeira]

Good catch!