SSL support

this is still WIP, but please review
see also #481

I'm able to connect to amazon rds using ssl:

```
var conn = require('node-mysql').createConnection({
  host     : 'xxxx.xxxxx.ap-southeast-2.rds.amazonaws.com',
  user     : 'xxxx',
  password : 'xxxx',
  port     : '3306',
  database : 'xxx',
  ssl      : 'Amazon RDS'
});

conn.query("show status like 'Ssl_cipher';", console.log);
```
output:
```
null [ { Variable_name: 'Ssl_cipher', Value: 'AES256-SHA' } ] [ { catalog: 'def',
    db: 'information_schema',
    table: 'STATUS',
    orgTable: 'STATUS',
    name: 'Variable_name',
    orgName: 'VARIABLE_NAME',
    filler1: <Buffer 0c>,
    charsetNr: 33,
    length: 192,
    type: 253,
    flags: 1,
    decimals: 0,
    filler2: <Buffer 00 00>,
    default: undefined,
    zeroFill: false,
    protocol41: true },
  { catalog: 'def',
    db: 'information_schema',
    table: 'STATUS',
    orgTable: 'STATUS',
    name: 'Value',
    orgName: 'VARIABLE_VALUE',
    filler1: <Buffer 0c>,
    charsetNr: 33,
    length: 3072,
    type: 253,
    flags: 0,
    decimals: 0,
    filler2: <Buffer 00 00>,
    default: undefined,
    zeroFill: false,
    protocol41: true } ]
```
Things left to do:
 - documentation
 - connect/disconnect streams2 properly using unpipe/pipe ( see TODO  comments in the code )

otherwise it looks like ssl is fully functional

Not sure if there is a way to have ssl tested with travis mysql setup. Any suggestions?