RFR: JDK-8153243: JShell: make docs --- should generate JShell API docs

[Jan Lahoda]

Hi,

Bug:
https://bugs.openjdk.java.net/browse/JDK-8153243

Javadoc for JShell API should be part of the "make docs".

Changes to the top-level repository:
http://cr.openjdk.java.net/~jlahoda/8153243/webrev.00/top-level/

Small tweaks to the langtools repository (JShell API javadoc) to avoid 
errors when building the javadoc:
http://cr.openjdk.java.net/~jlahoda/8153243/webrev.00/langtools/

Thanks,
     Jan