README cleanups

Hello everyone, I just started playing around with Tor a few days back so as one could expect I started with README.1st.md file. I realized that different *.md files are not consistent style-wise so I decided to clean them up a bit.

Brief summary:

• no empty line at the very beginning of the file,
• single empty line between sections (sometimes there were two)

... end of the sentence.

New Section
----

rather than

... end of the sentence.


New Section
----

• external links use name format,
• there is no single space in front of the section name

 Foo
===

is changed to

Foo
===

Which fixes syntax issues in editors like GNU Emacs with enabled markdown preview.

• I tried to check all links (local and external) and fix the ones which were broken.

For example the Tor proposal process inside README.1st.md or doc/WritingTests.txt were changed to .../doc/HACKING/WritingTests.md in few places).

---

At the very end of README.1st.md file there are some TODO (I think?) sections. I wrapped them around in "TODO" section.

TODO
-----------------------

XXXXX also describe

doc/HACKING/WritingTests.md

torguts.git

torspec.git

The design paper

freehaven.net/anonbib

XXXX describe these and add links.

However I am not sure if these are still needed there. Most of these topics are mentioned already in this file and linked to other files (WritingTests, torspec, etc.).