Rework textDocument/signatureHelp

- Proper handling of markdown parameter docs.
- Don't assume that function signatures have an `(` and `)`.
- Put the *active parameter docs* at the top, font-size 1rem.
- Put the *signature docs* under that, font-size 0.9rem.
- Use 0.9rem font-size for the intro message.
- KISS.

plugin/core/protocol.py

@@ -10,7 +10,7 @@
 TextDocumentSyncKindIncremental = 2
 
 
-class DiagnosticSeverity(object):
+class DiagnosticSeverity:
     Error = 1
     Warning = 2
     Information = 3
@@ -26,13 +26,19 @@ class InsertTextFormat:
     Snippet = 2
 
 
-class DocumentHighlightKind(object):
+class DocumentHighlightKind:
     Unknown = 0
     Text = 1
     Read = 2
     Write = 3
 
 
+class SignatureHelpTriggerKind:
+    Invoked = 1
+    TriggerCharacter = 2
+    ContentChange = 3
+
+
 ExecuteCommandParams = TypedDict('ExecuteCommandParams', {
     'command': str,
     'arguments': Optional[List[Any]],
@@ -56,6 +62,34 @@ class DocumentHighlightKind(object):
 })
 
 
+ParameterInformation = TypedDict('ParameterInformation', {
+    'label': Union[str, List[int]],
+    'documentation': Union[str, Dict[str, str]]
+}, total=False)
+
+
+SignatureInformation = TypedDict('SignatureInformation', {
+    'label': str,
+    'documentation': Union[str, Dict[str, str]],
+    'parameters': List[ParameterInformation]
+}, total=False)
+
+
+SignatureHelp = TypedDict('SignatureHelp', {
+    'signatures': List[SignatureInformation],
+    'activeSignature': int,
+    'activeParameter': int,
+}, total=False)
+
+
+SignatureHelpContext = TypedDict('SignatureHelpContext', {
+    'triggerKind': int,
+    'triggerCharacter': str,
+    'isRetrigger': bool,
+    'activeSignatureHelp': SignatureHelp
+}, total=False)
+
+
 class Request:
 
     __slots__ = ('method', 'params', 'view')