Format ObjC comment docs as Cocoadocs

Point RouteGuide pods to local sources; update requirements

Mark WaitForInitialMetadata as override, for Clang

Still needs implementing format_as_block, and switching input and output
to use sys.stdin.readline() and sys.stdout.write(line).

Fix auth sample

Make testing saner

Fix hello world example

Git ignore XCode derived files across the repo

Remove a few more linuxbrew references

PHP: update package.xml to prepare for 0.6.1 release

Backport run_tests.py shebang fix from master

Fix #2275 (Make sure PHP example can be run with Apache)

Normal constants, like most other things, are cleaned up during
RSHUTDOWN.
We need to explicitly mark them as persistent using CONST_PERSISTENT

"gRPC in 3 minutes" for Python