* travis: Add linter to make sure all lines end with a newline character
Ending newlines make line based Unix tools such as `tail`, etc work as expected.
Without ending newline:
```
prompt$ tail -1 ch02.asciidoc
* blockchain to save all transactions vs blockchain as a court system prompt$
```
With ending newline:
```
prompt$ tail -1 ch02.asciidoc
* blockchain to save all transactions vs blockchain as a court system
prompt$
```
Also, makes `git` not complain about "No newline at end of file" in diffs.
* Add newline at end of file
* Remove trailing whitespace
* travis: Add linter to make sure Unix style line endings are used
* Fix typos
* travis: Add linter to detect trailing spaces at end of line
* Remove trailing whitespace
* Use consistent indentation
* travis: Add linter guarding against use of tabs