5.0 release

Refactor eldoc (#448)

* Refactor eldoc

* Rename lsp-symbol-highlight to lsp-document-highlight
  We should keep consistency with LSP names
* Delete lsp-enable-codeaction
  It does not make sense to update codeAction again and again in eldoc
  They can add it to lsp-eldoc-hook if they really want the feature
* Delete lsp-hover-text-function, lsp-enable-eldoc, lsp-highlight-symbol-at-point in favor of lsp-eldoc-hooks
  lsp-ui-doc users are not affected.
* Add defcustom lsp-eldoc-hook to customize requests to send (default: documentHighlight, hover)
* Use add-function instead of setq to set eldoc-documentation-function

* Bump to 5.0