Updates appveyor.yml.

Related: #1096

Be explicit about which runtime versions travis should test

Use new libsass GitHub link

In case of exception occuring during construction
of a Sass type instance just return Undefined value,
as the delayed JS exception will pop up later.

The following code:

    var sass = require('./');
        sass.render({
        data: 'div { color: foo(); }',
          functions: {
            'foo()': function() {
              return sass.types.Color(2,3);
            }
          }
    });

now results in an libsass error

     Constructor should be invoked with either 0, 1, 3 or 4 arguments

instead of V8 abort

     FATAL ERROR: v8::ToLocalChecked Empty MaybeLocal

Instrument spec.js for test coverage
measurement.

Additional tests for SassTypes::Color

Update bindings for io.js 3.0.0

Use TypeError whenever argument count
or type do not match and RangeError
if the index is out of bounds.

The value is not returned, it is passed on
to another funcion.

nan 2.0.1 required due to introduction
of Nan::NewInstance(v8::Local<v8::Function)>, int, v8::Local<v8::Value>)
constructor:

    https://github.com/nodejs/nan/commit/29450ed1670051613ffea9dd3f980f8685feceb4

Master

Added note to indentedSyntax in read.me 

Added note to indentedSyntax in read.me to clarify that node-sass can compile mixed libraries even with this set to false.

The watcher should watch indented syntax files too

This fixes a bug that prevented the watcher from triggering file
compilations on changes to .sass file.

Fixes #1075

Locate pangyp via module API

Use Nan::To<Type> instead of ->ToType() to
convert caller supplied objects in renderXXX
functions.

Verify that provided options, options.result
and options.result.stats are all valid
objects provided by the caller.
Throw TypeException otherwise.

Introduce low-level tests that invoke
C++ function directly, without additional
JavaScript wrappers.

TROUBLESHOOTING.md: Windows: Use "npm install -ddd"

- Use "npm install -ddd"
- Capture logfiles
- Provide known-good reference logfiles
  for comparison

No need to have EscapableHandleScope, since local
handle is not returned by the method - only
assigned to an objects supplied by the caller.

For bool, double, [u]int32_t there is no need to wrap
a returned value in Nan::New()

https://github.com/nodejs/nan/blob/master/doc/methods.md#api_nan_return_value