Updates to thirdparty README and COPYRIGHT

Notably, we now track stable Bullet 2.88, so distros can
unbundle it again.

thirdparty/README.md

@@ -19,7 +19,7 @@ comments.
 ## bullet
 
 - Upstream: https://github.com/bulletphysics/bullet3
-- Version: git (126b676, 2018-12-31)
+- Version: 2.88
 - License: zlib
 
 Files extracted from upstream source:
@@ -255,7 +255,7 @@ changes are marked with `// -- GODOT --` comments.
 ## libwebsockets
 
 - Upstream: https://github.com/warmcat/libwebsockets
-- Version: 3.0.0
+- Version: 3.0.1
 - License: LGPLv2.1 + static linking exception
 
 File extracted from upstream source:
@@ -292,10 +292,11 @@ File extracted from upstream release tarball `mbedtls-2.16.0-apache.tgz`:
 ## miniupnpc
 
 - Upstream: https://github.com/miniupnp/miniupnp/tree/master/miniupnpc
-- Version: 2.1 (git 25615e0, 2018-05-08) with modifications
+- Version: git (25615e0, 2018)
 - License: BSD-3-Clause
 
-The only modified file is miniupnpcstrings.h, which was created for Godot (is usually autogenerated by cmake).
+The only modified file is miniupnpcstrings.h, which was created for Godot
+(it is usually autogenerated by cmake).
 
 
 ## minizip
@@ -380,7 +381,7 @@ Collection of single-file libraries used in Godot components.
 
 - `ifaddrs-android.{cc,h}`
   * Upstream: https://chromium.googlesource.com/external/webrtc/stable/talk/+/master/base/ifaddrs-android.h
-  * Version: 5976650 (2013)
+  * Version: git (5976650, 2013)
   * License: BSD-3-Clause
 
 ### scene