Fix comments
Merge pull request #171 from colmmacc/doc

/dev/random -> /dev/urandom nit fix
Add a book.json file to fix the link to the doc source
Merge branch 'doc' of github.com:jedisct1/libsodium into doc

* 'doc' of github.com:jedisct1/libsodium:
  /dev/random -> /dev/urandom nit fix
Use the correct tense of open and keep

Minor language fix: "it opens" ... "it keeps"
Add a note about non-memcmp compatibility

sodium_memcmp is really an equality tester, rather than a replacement
for memcmp, add a warning note for implementors.
() after a function name, for consistency
Add a note about mlock() failure due to ulimits
Quotes
Minor tense fix for set

"it sets" ...
Merge remote-tracking branch 'upstream/doc' into doc

Conflicts:
	doc/helpers/README.md
Lenghtier note on nonce practices