Feature request: Forward options to ts-morph

**Do you want to request a _feature_ or report a _bug_?**
Feature: Forward options to ``ts-morph``.

**What is the current behavior?**
``docs-ts`` provides ``{"strict": true}`` as configuration to the ``ts-morph`` project.

**Use case**
I want to provide a non-default ``tsconfig.json`` to ``ts-morph``, but this is not possible, because ``docs-ts`` provides a fixed config. ``ts-morph`` itself would allow a `different configfile name.

This makes ``docs-ts`` hard to use, in case the own project uses a ``tsconfig.json`` which isn't compatible with ``node`` (my concrete case is, that I can't find a ``module`` option, that satisfies ``webpack``'s ``ts-loader`` and ``docs-ts`` and also ``ts-loader`` is really unhappy, if I tell it to use a different ``tsconfig.json``).

**What is the expected behavior?**
Add an optional entry ``"ts-morph"`` to ``docs-ts.json``, which is forwarded to ``ts-morph``.

**Which versions of docs-ts, and which browser and OS are affected by this issue? Did this work in previous versions of docs-ts?**
All. (Using ``0.6.10``)

I'm willing to implement this, if it has the chance to be merged.

Oh: And btw: @gcanti: I love your typescript work. Thank you so much. :-)

Start by tracing how docs-ts reads docs-ts.json and creates the ts-morph project; no specific files or tests are named in the issue. Verify that an optional "ts-morph" configuration entry is forwarded while the existing default remains unchanged, and test it with a non-default tsconfig.json.

Written by the indexing model from the issue text.