Generate docs index from header file structure (#6)

Use Clang JSON to navigate and xref the header files to the Swift types.

Add to J2 and DocC docs metadata.

Author: johnfairh

.jazzy.yaml

@@ -0,0 +1,4 @@
+version: 1
+builder:
+  configs:
+    - documentation_targets: [Steamworks, SteamworksHelpers, SteamworksEncryptedAppTicket]

.spi.yml

@@ -0,0 +1,38 @@
+## Topics
+
+### API Clients
+- ``SteamBaseAPI``
+- ``SteamAPI``
+- ``SteamGameServerAPI``
+- ``SteamEncryptedAppTicket``
+### Interfaces
+- <doc:SteamAppList-Interface>
+- <doc:SteamApps-Interface>
+- <doc:SteamFriends-Interface>
+- <doc:SteamGameSearch-Interface>
+- <doc:SteamGameServer-Interface>
+- <doc:SteamGameServerStats-Interface>
+- <doc:SteamHTMLSurface-Interface>
+- <doc:SteamHTTP-Interface>
+- <doc:SteamInput-Interface>
+- <doc:SteamInventory-Interface>
+- <doc:SteamMatchmaking-Interface>
+- <doc:SteamMatchmakingServers-Interface>
+- <doc:SteamMusic-Interface>
+- <doc:SteamMusicRemote-Interface>
+- <doc:SteamNetworkingMessages-Interface>
+- <doc:SteamNetworkingSockets-Interface>
+- <doc:SteamNetworkingUtils-Interface>
+- <doc:SteamParentalSettings-Interface>
+- <doc:SteamParties-Interface>
+- <doc:SteamRemotePlay-Interface>
+- <doc:SteamRemoteStorage-Interface>
+- <doc:SteamScreenshots-Interface>
+- <doc:SteamUGC-Interface>
+- <doc:SteamUser-Interface>
+- <doc:SteamUserStats-Interface>
+- <doc:SteamUtils-Interface>
+- <doc:SteamVideo-Interface>
+### Common Types
+- <doc:Common-Types>
+- ``SteamConstants``