Automatically check documentation for compile errors

[dsherret]

It should be very easy to check the documentation for compile errors. I don't think this needs to be that flexible. The following should be beneficial enough for now:

1. Grab all the code out of the .md files by looking for the three backticks.
2. For each code section concatenate with some global code that types some variables used in the documentation. Check each source file for errors and output where they occur.

Edit (2018-04-17): I'll probably be moving and improving this functionality out into a library sometime

Edit (2018-07-21): Using "configuration comments" (https://github.com/eslint/eslint-plugin-markdown) would probably be a better idea than storing meta-data in the first line of the code block.

[dsherret]

Important to note that meta-data seems to be allowed to be stored after the specified language in the info string: https://github.github.com/gfm/#example-112

That could be used for defining the setup for a code block.

[dsherret]

This currently only works in ts or typescript code blocks.

Example using a "setup" for the code block:

```ts setup: let grandParentDir: Directory, childDir: Directory;
grandParentDir.isAncestorOf(childDir);   // true
childDir.isDescendantOf(grandParentDir); // true
````

Example of ignoring a compile error:

```ts ignore-error: 1109
// given an existing node and type checker
const classNode: ts.ClassDeclaration = ...;
const compilerTypeChecker: ts.TypeChecker = ...;

// etc...
````

It also uses this file to define all the globals: https://github.com/dsherret/ts-simple-ast/blob/master/docs/_script-templates/main.ts

[dsherret]

Hmmm... seems like github is not following https://github.github.com/gfm/#example-112 for how markdown should be displayed on github pages.

Edit: I emailed github pages support.

[dsherret]

GitHub pages gave a very helpful reply. I need to add markdown: GFM to _config.yml.

[dsherret]

This is all done now and the markdown files in this library have type checking in them.

Overall, found 19 bugs in the documentation... and surprisingly 2 bugs in the library (this and this).