Replace relative image paths with URL to tagged image

This is being done so that images will work in the 2.0.0 release
published to PyPI. Images do not load from a README in PyPI if they
are relative paths to files in the repository, so a URL is being
used instead. Moreover, the URL contains the v2.0.0 tag in the
path. This will ensure that even if the images change or are
deleted in the future, the published version will display the
images from publication time.

These changes are only intended for PyPI, so the commit will be
rolled back beyond the tag commit.

README.md

@@ -8,7 +8,7 @@ visualize the graph, or a JSON structure that you can consume with
 other software tools. Here's an example of a genealogy built by
 Geneagrapher and visualized using Graphviz:
 
-<img src="/images/chioniadis-geneagraph.png" alt="Chioniadis math
+<img src="https://raw.githubusercontent.com/davidalber/geneagrapher/v2.0.0/images/chioniadis-geneagraph.png" alt="Chioniadis math
 genealogy" width="480px">
 
 To use this package, you will need to have a Python interpreter on
@@ -119,7 +119,7 @@ the file zwinger.dot, run the command
 ggrapher -o zwinger.dot 125148:a
 ```
 
-![Zwinger math genealogy](images/zwinger-geneagraph.png)
+![Zwinger math genealogy](https://raw.githubusercontent.com/davidalber/geneagrapher/v2.0.0/images/zwinger-geneagraph.png)
 
 ### Multiple Node Ancestry: Petrus Ryff and Theodor Zwinger
 To produce the combined ancestry DOT file for Petrus Ryff and Theodor
@@ -129,7 +129,7 @@ Zwinger and save it in the file ryff_zwinger.dot, run the command
 ggrapher -o ryff_zwinger.dot 125148:a 130248:a
 ```
 
-![Ryff-Zwinger math genealogy](images/ryff-zwinger-geneagraph.png)
+![Ryff-Zwinger math genealogy](https://raw.githubusercontent.com/davidalber/geneagrapher/v2.0.0/images/ryff-zwinger-geneagraph.png)
 
 ### Single Node Descendant Graph: Haskell Curry
 To produce the descendant DOT file for Haskell Curry and save it in
@@ -139,7 +139,7 @@ the file curry.dot, run the command
 ggrapher -o curry.dot 7398:d
 ```
 
-![Curry math genealogy descendants](images/curry-geneagraph.png)
+![Curry math genealogy descendants](https://raw.githubusercontent.com/davidalber/geneagrapher/v2.0.0/images/curry-geneagraph.png)
 
 Note that descendant graphs often have a lot of "fan out".