Fix lint found in melpa PR

[arobertn]

I'm attempting to add this package to Melpa. There are a few linting steps to be carried out, as documented in the PR's template description and the CONTRIBUTING doc.

This PR addresses some of the problems found:

• Add daml-lsp.el to the package-lint and compile targets in the Makefile so warnings are picked up from them.
• Add formal license references to the elisp file headers.
• Add / format some doc strings

The following problems remain (see output here) as I'm not sure how to fix them:

• If you run package-lint-current-buffer on either of the files, you get "file not found errors". (Ignoring since running it programmatically with through make package-lint works fine.
• package-lint gives '"lsp-daml--..." doesn't start with package's prefix "daml"' warnings. (Ignoring because this seems to be a lsp client mode naming convention.)
• Byte-compiling daml-lsp.el generates warnings around the lsp-interface function: "attempt to let-bind constant" and "reference to free variable". I don't see this warning when compiling uses of lsp-interface in the lsp client modes built in to the lsp-mode distribution (e.g. Clojure, PHP).

[bartfailt]

Hello @arobertn , thanks for the helping hand! This project needs some love, as there are other issues with the as well. I will try to find some time, hopefully this week to address them.