Added link to push notification guide and did minor formatting changes.
Fixed three example source code links.
Updated outdated info in push notification guides and added important note about Android message contents
Added missing punctuation
Merge pull request #1 from Sionarch/ThreeThreeOne

[MOSYNC-3337, MOSYNC-3334] Push notification guides corrections
Merge remote-tracking branch 'origin/ThreeThreeOne' into ThreeThreeOne
Merge pull request #20 from divineprog/ThreeThreeOne

[MOSYNC-3337] Fix of broken links and punctuation