Add InfluxQL scanner.

This commit adds a pure Go implementation of the InfluxQL scanner. It includes support for:

- Identifiers
- Numbers
- Strings
- Durations
- Booleans
- Numeric and logical operators
- InfluxQL keywords
Merge branch 'master' of https://github.com/influxdb/influxdb into scanner
CHANGELOG
Fix EQ token scanning.
Fix Scanner.Scan() comment.
Add semicolon, INSERT, INTO to Scanner.
Merge pull request #1151 from influxdb/scanner

Scanner