first try and sort-of works

try:

----------

require 'rubygems'
require 'vips'

include VIPS

data = IO.read('/home/john/pics/shark.jpg')

reader = JPEGReader.new(data, :shrink_factor => 2, :fail_on_warn =>
true)

im = reader.read_buffer

im.write('out.png')
----------
cleanups for new buffer read

use vips8 API for buffer read/write stuff, if possible, it improves
compatibility

fix an oops in version #if-ing
Ooops argh

another compat oops fixup
README oops
add png memory load

needs vips-7.34 or later

also improved vips lib version testing
add spec tests for buffer load

the new png and jpg load from buffer paths now have spec tests