First, it removes the documentation section from all the README.md files
and instead puts a web-based godoc badge and link at the top with the
other badges. This is being done since the local godoc tool no longer
ships with Go by default, so the instructions no longer work without
first installing godoc. Due to this, pretty much everyone uses the
web-based godoc these days anyways. Anyone who has manually installed
godoc won't need instructions.
Second, it makes sure the ISC license badge is at the top with the other
badges and removes the textual reference in the overview section.
Third, it's modifies the Installation section to Installation and
Updating and adds a -u to the go get command since it works for both and
thus is simpler.
Finally, it replaces the badges with SVG versions from shields.io so
they are consistent.
This converts the txsort code into a separate package and renames
'TxSort' and 'IsTxSorted' to 'Sort' an `IsSorted`, respectively.
It also adds a 'doc.go' and 'README.md' so it is consistent with the
other packages.
