Fix spelling and grammar in README

Trivial Patch
Add a custom logger level for "internal omnibus" messages

Prior to this commit, there was a conflation between an Omnibus debug
message and a build debug message. This commit adds a new log level
called "internal" that is more verbose than debug.
Add "nothing" log level for seriously nothing
Do not use a lazy_default for the log level
Improve the logging semantics
Use double quotes for DSL files
Update CHANGELOG for 4.0.0 [ci skip]