(SIMP-344) Add 4.2.0-beta2 changelog

This commit removes Publican documentation and provides a cumulative
summary of all user-relevant changes to the 4.2.0 build process in the
document "Changelog.rst."

SIMP-28  #comment Removed publican documentaton.
SIMP-344 #close #comment Added 4.2.0-beta2 changelog.
SIMP-347 #comment Embedded readthedocs theme into rst docs (license:MIT)
SIMP-4   #comment Added 4.2.0-beta2 changelog.
SIMP-4   #comment Added docs:html task to Rakefile
SIMP-4   #comment Updated conf.py to infer 'simp_#' tag based on version

Change-Id: I5c6736908b7dcb3a0074db68058abbf4a1f60ea0

.gitignore

@@ -0,0 +1,6 @@
+rst/_build
+docs/_build
+_build_v5
+_build_v4
+.sw[pnoqst]
+builderrors

.travis.yml

@@ -0,0 +1,9 @@
+# build reStructuredText documentation
+---
+language: python
+python:
+  - "2.7"
+install: "pip install -q -r requirements.txt --use-mirrors"
+script:
+  - sphinx-build -n -t simp_4 -b html -d _build_v4/sphinx_cache docs/ _build_v4/html
+  - sphinx-build -n -t simp_5 -b html -d _build_v5/sphinx_cache docs/ _build_v5/html