typing: Convert function type annotations to Python 3 style.

Generated by com2ann (slightly patched to avoid also converting
assignment type annotations, which require Python 3.6), followed by
some manual whitespace adjustment, and two fixes for use-before-define
issues:

-    def set_zulip_client(self, zulipToJabberClient: ZulipToJabberBot) -> None:
+    def set_zulip_client(self, zulipToJabberClient: 'ZulipToJabberBot') -> None:

-def init_from_options(options: Any, client: Optional[str] = None) -> Client:
+def init_from_options(options: Any, client: Optional[str] = None) -> 'Client':

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

tools/review

@@ -3,36 +3,30 @@
 import subprocess
 import sys
 
-def exit(message):
-    # type: (str) -> None
+def exit(message: str) -> None:
     print('PROBLEM!')
     print(message)
     sys.exit(1)
 
-def run(command):
-    # type: (str) -> None
+def run(command: str) -> None:
     print('\n>>> ' + command)
     subprocess.check_call(command.split())
 
-def check_output(command):
-    # type: (str) -> str
+def check_output(command: str) -> str:
     return subprocess.check_output(command.split()).decode('ascii')
 
-def get_git_branch():
-    # type: () -> str
+def get_git_branch() -> str:
     command = 'git rev-parse --abbrev-ref HEAD'
     output = check_output(command)
     return output.strip()
 
-def check_git_pristine():
-    # type: () -> None
+def check_git_pristine() -> None:
     command = 'git status --porcelain'
     output = check_output(command)
     if output.strip():
         exit('Git is not pristine:\n' + output)
 
-def ensure_on_clean_master():
-    # type: () -> None
+def ensure_on_clean_master() -> None:
     branch = get_git_branch()
     if branch != 'master':
         exit('You are still on a feature branch: %s' % (branch,))
@@ -40,8 +34,7 @@ def ensure_on_clean_master():
     run('git fetch upstream master')
     run('git rebase upstream/master')
 
-def create_pull_branch(pull_id):
-    # type: (int) -> None
+def create_pull_branch(pull_id: int) -> None:
     run('git fetch upstream pull/%d/head' % (pull_id,))
     run('git checkout -B review-%s FETCH_HEAD' % (pull_id,))
     run('git rebase upstream/master')
@@ -53,8 +46,7 @@ def create_pull_branch(pull_id):
     print(subprocess.check_output(['git', 'log', 'HEAD~..',
                                    '--pretty=format:Author: %an']))
 
-def review_pr():
-    # type: () -> None
+def review_pr() -> None:
     try:
         pull_id = int(sys.argv[1])
     except Exception: