Update Version() to point to the correct web addresses.

For classic AviSynth, this is http://avisynth.nl
For AviSynth+, it's http://avs-plus.net
README: use markdown, fix syntax, and add stuff

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Fix: Typo in TemporalSoften.
IsPtrAligned() and AlignPointer() interface fix.
Merge branch 'versionfix' of https://github.com/qyot27/avisynth into wip
Add "last" variable upon environment initialization. Some filters depend on its constant existence.
Merge branch 'patch-1' of https://github.com/TimothyGu/avisynth into wip
Change printed version string format.
Fix: 'return' was only returning from the inner-most block.
Add rastered icon pages. Some of these have been hand-edited after being rasterized from the vector versions.