Feature Request: Ignore YAML Metadata

[zeroSteiner]

Prerequisites

• [ ] Reproduced the problem in Safe Mode (may not be appropriate if your error involves markdown-preview-plus): http://flight-manual.atom.io/hacking-atom/sections/debugging/#using-safe-mode
• [x] Checked that the issue isn't already filed: https://github.com/travs/markdown-pdf/issues)

Issue description

This is a request for a feature to ignore YAML metadata in markdown files. A few systems (pandoc, GitHub) support having metadata defined in YAML in markdown files. The metadata is delimited by three dashes --- followed by valid YAML and then terminated with three dashes again.

Right now this metadata shows up as a table at the top of the document. It would be really nice if there was an option to have this metadata simply hidden from both the preview and the PDF output.

Steps to reproduce

Expected behavior: Add a YAML metadata field at the top of the markdown document and see no additional content in the preview or PDF.

Actual behavior: Add a YAML metadata field at the top of the markdown document and see it in a table.

Input

This is a copy of a feature request template I use in one of my GitHub projects. The YAML metadata is at the top and was generated using GitHub's issue template creator.

---
name: Feature Request
about: Suggest an idea for this project

---

# Feature Description
<!-- Describe the feature here that you would like to see added to the project. Does the feature solve a problem and how often do you think it will be used? -->

## Alternatives Solutions
<!-- Describe any alternative solutions you considered and why you came to the conclusion you did regarding the proposed solution. -->

## Example Use Case
<!-- Provide an example of when this feature would be used. -->

Versions

You can get this information from copy and pasting the output of atom --version and apm --version from the command line. Also, please include the OS and what version of the OS you're running.

Atom    : 1.24.1
Electron: 1.6.16
Chrome  : 56.0.2924.87
Node    : 7.4.0

[travs]

Tracking here: https://github.com/BlueHatbRit/mdpdf/issues/88