Expand snippet with longest prefix

Previously a custom word regex was used to find the snippet prefix
but that causes issues when non-word characters are used as the snippet
prefix.
:lipstick: Rename e to event
:memo: Remove prefix limitations
Include all snippets from atom.syntax properties
Add spec for bad prefix
:lipstick: Simplify diff by keeping method location
Rename getWordRegex to wordRegexForSnippets
Check for empty selection in expandSnippetUnderCursor
:lipstick: Make event handlers multiine consistent
Merge pull request #31 from atom/ks-match-longest-prefix

Match snippet with longest prefix