feat: tangle

[danilshvalov]

This PR develops ideas #435 (part of the code was taken right from there). In this PR, I implemented inheritance of properties for code blocks and headings.

Examples

All the following examples tangle code block to test.lua:

1. Document property:

   #+PROPERTY: header-args :tangle test.lua
   
   #+begin_src lua
   local foo = "bar"
   #+end_src
   

2. Heading property:

   * Heading
   :PROPERTIES:
   :tangle: test.lua
   :END:
   
   #+begin_src lua
   local foo = "bar"
   #+end_src
   

   or

   * Heading
   :PROPERTIES:
   :header-args: :tangle test.lua
   :END:
   
   #+begin_src lua
   local foo = "bar"
   #+end_src
   

3. Code block property:

   #+begin_src lua :tangle test.lua
   local foo = "bar"
   #+end_src
   

TODO

• Use queries instead of recursion
• Remove magic constants
• Add tests
• Add documentation

[kristijanhusak]

Some support was added in #685. We can build up on that. Closing this.
Thanks for the PR anyway!