Typos and grammar fixes through chapter 4.
Merge pull request #35 from bentley/dox

Typos and grammar fixes through chapter 4.
workaround for OpenBSD 'stdin' implementation
workaround for OpenBSD 'stdout' implementation
Improved ezsat stand-alone tests
Progress in presentation
Updated ABC to 67c84cdd49e4
Merge branch 'master' of github.com:cliffordwolf/yosys
fixed syntax error in dot file created by "show" command
Fixed bug in opt_reduce (see vloghammer issue_044)