RFR [9] 8132468: docs: replace <tt> tags (obsolete in html5) for java.io, java.lang, java.math

[Alexander Stepanov]

Hello,

Could you please review the following fix:
http://cr.openjdk.java.net/~avstepan/8132468/webrev.00/
for
https://bugs.openjdk.java.net/browse/JDK-8132468

Just some cleanup for docs (replacing obsolete "<tt></tt>").

Thanks,
Alexander