Expand and organize .gitignore
Expand and organize .gitignore

Change-Id: Ic6efa8a33e71b96731ecf0ca5d6ab45baccf6d5a

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed