README: Remove double spaces
testing.txt: Change order of text, update syntax.
add "|" around branch name to match other one
fix list punctuation
explain "on hold" GH issue label
simplify discussion of scc dependencies in Python
Merge pull request #451 from sbesson/homebrew_default_ice

Update Homebrew installation page to expose Ice 3.4 as the default version
merge dev_4_4 -D org -I include -E exclude: PR 261 (Generate PDF using XeLaTeX)
merge dev_4_4 -D org -I include -E exclude: PR 368 (Cpp: Correct content and markup)
merge dev_4_4 -D org -I include -E exclude: PR 454 (Expand the title of the "writing tests" page)
merge dev_4_4 -D org -I include -E exclude: PR 455 (Clean up testing.txt)
merge dev_4_4 -D org -I include -E exclude: PR 456 (Adjusted titles of continuous integration developer pages)