snakebin: misc cleanup and fixes

Typo fixes, rst fixes, example code fixes, clarifications, etc.
Merge pull request #48 from larsbutler/snakebin-fixes

snakebin: misc cleanup and fixes
snakebin: remove stderr/log device
Merge pull request #49 from larsbutler/snakebin-fixes-2

snakebin: remove stderr/log device
zerovm: fix a typo in channel docs
snakebin: fix zapp.yaml syntax highighting
Merge pull request #52 from larsbutler/fix-snakebin-syntax-highlight

snakebin: fix zapp.yaml syntax highighting
snakebin: fix a broken curl command
Merge pull request #50 from larsbutler/channels-typo

zerovm: fix a typo in channel docs
Merge pull request #53 from larsbutler/fix-snakebin-post-command

snakebin: fix a broken curl command