Split up main.py (sublimelsp#170)

`boot.py` loads modules under the `plugin` and `plugin/core` folders.

Author: tomv564

.travis.yml

@@ -5,5 +5,5 @@ before_install:
     - pip install mypy
     - pip install flake8
 script:
-    - mypy main.py
-    - flake8
+    - mypy -p plugin
+    - flake8 --exclude=./boot.py

boot.py

@@ -0,0 +1,25 @@
+from .plugin.core.main import startup, shutdown, LspStartClientCommand, LspRestartClientCommand
+
+# TODO: narrow down imports
+from .plugin.core.panels import *
+from .plugin.core.documents import *
+from .plugin.core.edit import *
+from .plugin.completion import *
+from .plugin.diagnostics import *
+from .plugin.configuration import *
+from .plugin.formatting import *
+from .plugin.definition import *
+from .plugin.hover import *
+from .plugin.references import *
+from .plugin.signature_help import *
+from .plugin.code_actions import *
+from .plugin.symbols import *
+from .plugin.rename import *
+
+
+def plugin_loaded():
+    startup()
+
+
+def plugin_unloaded():
+    shutdown()