Support dl, dt, dd tags in Erlang HTML docs

[fhunleth]

Here's the stack trace:

** (FunctionClauseError) no function clause matching in NextLS.HoverHelpers.to_markdown/2
    (next_ls 0.16.0) lib/next_ls/helpers/hover_helpers.ex:6: NextLS.HoverHelpers.to_markdown("application/erlang+html", [{:dl, [], [{:dt, [], [{:code, [], ["root"]}]}, {:dd, [], [{:p, [], ["The installation directory of Erlang/OTP, ", {:code, [], ["$ROOT"]}, ":"]}, {:pre, [], [{:code, [], ["2> init:get_argument(root).\n{ok,[[\"/usr/local/otp/releases/otp_beam_solaris8_r10b_patched\"]]}"]}]}]}, {:dt, [], [{:code, [], ["progname"]}]}, {:dd, [], [{:p, [], ["The name of the program which started Erlang:"]}, {:pre, [], [{:code, [], ["3> init:get_argument(progname).\n{ok,[[\"erl\"]]}"]}]}]}, {:dt, [], [{:a, [id: "home"], []}, {:code, [], ["home"]}]}, {:dd, [], [{:p, [], ["The home directory (on Unix, the value of $HOME):"]}, {:pre, [], [{:code, [], ["4> init:get_argument(home).\n{ok,[[\"/home/harry\"]]}"]}]}]}]}, {:p, [], ["Returns ", {:code, [], ["error"]}, " if no value is associated with ", {:code, [], ["Flag"]}, "."]}])
    (next_ls 0.16.0) lib/next_ls/helpers/hover_helpers.ex:9: NextLS.HoverHelpers.to_markdown/2
    (next_ls 0.16.0) lib/next_ls/helpers/hover_helpers.ex:34: NextLS.HoverHelpers.to_markdown/2
    (next_ls 0.16.0) lib/next_ls/helpers/hover_helpers.ex:9: NextLS.HoverHelpers.to_markdown/2
    (next_ls 0.16.0) lib/next_ls.ex:365: NextLS.handle_request/2
    (gen_lsp 0.7.1) lib/gen_lsp.ex:271: anonymous fn/2 in GenLSP.loop/3
    (telemetry 1.2.1) /private/tmp/cirrus-ci/working-dir/deps/telemetry/src/telemetry.erl:321: :telemetry.span/3
    (gen_lsp 0.7.1) lib/gen_lsp.ex:270: anonymous fn/6 in GenLSP.loop/3

To reproduce, call :init.get_argument(:boot) in an Elixir file and hover over it in VSCode.