sql-ast v0.3.0

The current goal of sql-ast is to parse the output of mysqldump into an AST.
If anyone wants to expand the capability of this library, feel free to send some
pull requests!

``js
const {parse} = require('sql-ast');

parse(input); // => [object Array]
`

Note: The current feature set is very limited. Open an issue if you have want
something that isn't supported yet.

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Tokens are not created for whitespace.

This includes spaces, tabs (\t), line breaks (\n), and carriage returns (\r).

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Tokens are not created for comments.

All three styles are supported: /*, --, and #.

One exception is /*!-style comments, which annotate the minimum MySQL version
required to run the statement(s) or apply the attribute(s) contained within.
Special version tokens are created for these comments.

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- word is a character group matching /^[a-z0-9_$]+$/i
- ident is a character group wrapped with backtick quotes
- punct is a character matching /^[(),.;=]$/
- string is a character group wrapped with single or double quotes
- number is a character group matching /^-?[0-9]+(\.[0-9]+)?(E-?[0-9]+)?$/
- variable is a character group matching /^@@?[$._a-z]+$/i
- version is a /!-style comment or its / closer

Every token has these properties:
- type: string
- value: string|number
- start: number
- end: number

#### Notes
- The value of a number is a number literal.
- The value of a ident or string does not include the quotes.
- The value of a version tells you the minimum MySQL version required
before any following tokens can be used. This remains in effect until another
version token is found.
- When the value of a version token is:
- > 0 a minimum version of MySQL is required
- == 0 no minimum version, but MySQL is required
- == -1 MySQL is not required

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Every AST node extends the Node class and has start and end properties.

Action nodes are typically owned by statements that perform actions (eg: ALTER).

Attribute nodes are typically owned by statements, column definitions, and index
definitions. Some examples are IF EXISTS and ENGINE=ISAM.

Column and Index nodes are owned by CREATE TABLE statements.

Literal and Variable nodes are created for value expressions.

Variable nodes are also created when a SET statement sets a variable.
In this case, the node has a value property.

Row nodes are owned by INSERT and REPLACE statements.

Statement nodes only exist in the top-level array returned by parse`.

#### Notes
- All node types are exported by the main module.
- They have no methods by default. Feel free to define methods as you see fit.
- More node types may be added in the future.