api: get_streams (#886)

## Link to GitHub Issue or related Pull Request, if one exists
#0

## Description of change
MSE method of streaming video needs the dimensions up front. This new
api delivers that. Also provides an easier way to determine which
screens are available and a way to discover port number.

## Testing
See pending changes in substream project

src/spice2x/api/resources/python/spiceapi/capture.py

@@ -0,0 +1,33 @@
+import base64
+
+from .connection import Connection
+from .request import Request
+
+
+def capture_get_screens(con: Connection):
+    res = con.request(Request("capture", "get_screens"))
+    return res.get_data()
+
+
+def capture_get_jpg(con: Connection, screen: int = 0, quality: int = 70, divide: int = 1):
+    req = Request("capture", "get_jpg")
+    req.add_param(screen)
+    req.add_param(quality)
+    req.add_param(divide)
+    data = con.request(req).get_data()
+
+    if len(data) < 4:
+        return None
+
+    return {
+        "timestamp": data[0],
+        "width": data[1],
+        "height": data[2],
+        "data": base64.b64decode(data[3]),
+    }
+
+
+def capture_get_streams(con: Connection):
+    """Describes the HTTP video stream, or None when this spice2x serves none."""
+    data = con.request(Request("capture", "get_streams")).get_data()
+    return data[0] if data else None