Add Disclaimer to README

This project got posted to news.ycombinator.com and got a lot of unwarranted attention because the description doesn't make it clear enough that this is not an official Google project. It's not "Google's Pyringe", it's just an intern's project that got open-sourced.
Change wording in CONTRIBUTING.md

In line with 1cec69023bc1d8d6f787f8f3f53b31ecb2c15d44, this is to make it clearer to readers that this is not a Google project, but the project of an individual who worked for Google.
Update README.md, specify python3-unfriendliness.
Bump required version of gdb to 7.4

It seems like `gdb.selected_inferior()` was only introduced after the release of 7.3.1. Partial functionality may or may not be available if you're running an earlier build.

(It's a shame the python API doc doesn't specify when they added which function)
Add version check to gdb and only enable --nh when available
Fix syntax mistake resulting in spurious exceptions.
Bump version to 1.0.1
Make gdb version detection more flexible.
Add another example for gdb's versionstring format
Bump version to 1.0.2
Add note about limitations of pyringe on Ubuntu

Ubuntu doesn't ship a symbol file with type information for the regular python executable (issue #19), so until that changes, Ubuntu users can only debug custom builds or the build included in the python-dbg package with pyringe.
Make symbol lookup more flexible and stable with partial debugging info
Add support for setting the target architecture from the repl
Add more logging

Also, provide a more obvious way of changing the log level from the
repl.
Merge pull request #1 from google/master

update