aproba
======
A ridiculously light-weight function argument validator
```
var validate = require("aproba")
function myfunc(a, b, c) {
// `a` must be a string, `b` a number, `c` a function
validate('SNF', arguments) // [a,b,c] is also valid
}
myfunc('test', 23, function () {}) // ok
myfunc(123, 23, function () {}) // type error
myfunc('test', 23) // missing arg error
myfunc('test', 23, function () {}, true) // too many args error
```
Valid types are:
| type | description
| :--: | :----------
| * | matches any type
| A | `Array.isArray` OR an `arguments` object
| S | typeof == string
| N | typeof == number
| F | typeof == function
| O | typeof == object and not type A and not type E
| B | typeof == boolean
| E | `instanceof Error` OR `null` **(special: see below)**
| Z | == `null`
Validation failures throw one of three exception types, distinguished by a
`code` property of `EMISSINGARG`, `EINVALIDTYPE` or `ETOOMANYARGS`.
If you pass in an invalid type then it will throw with a code of
`EUNKNOWNTYPE`.
If an **error** argument is found and is not null then the remaining
arguments are optional. That is, if you say `ESO` then that's like using a
non-magical `E` in: `E|ESO|ZSO`.
### But I have optional arguments?!
You can provide more than one signature by separating them with pipes `|`.
If any signature matches the arguments then they'll be considered valid.
So for example, say you wanted to write a signature for
`fs.createWriteStream`. The docs for it describe it thusly:
```
fs.createWriteStream(path[, options])
```
This would be a signature of `SO|S`. That is, a string and and object, or
just a string.
Now, if you read the full `fs` docs, you'll see that actually path can ALSO
be a buffer. And options can be a string, that is:
```
path |
options |