A few document clarifications for Java & Internals.

Change-Id: I770b53cf7d82c860422c1fe6193fb597d9c9495c
File identifier feature.

Allows you to add, and test for the presence of a magic 4-char
string in a FlatBuffer.

Tested: on OS X.

Change-Id: I090692a9e4fb53bed3543279a28563e67132cba0
Clarified a documentation statement about circular references.

Change-Id: I8f3c50085f89037995ab9f26b28d3c83667e9d6f
Schemas now support include files.

Bug: 15521443
Change-Id: I2e1ef97e7225a1a0ecf2ca65e31d49d443003747
Tested: on Linux.
Support all JSON escape codes (including \u) for parsing & text gen.

Bug: 16624362
Change-Id: Ia09ea404c0c11dd1dc6993a8cbd155bf8152b65f
Tested: on Windows & Linux.
Implemented the file identifier functionality for Java.

Also fixed flatc not outputting these identifiers for files
compiled on the command-line.

Bug: 16983987
Change-Id: I8b714cfea3a8e144fa52133f62b2f7eda6eb044a
Tested: on Linux
Added accessor in Java to get vectors as ByteBuffers.

Also cleaned up ByteBuffer usage in general: ByteBuffer.position
now universally indicates the start of a ByteBuffer.

Change-Id: Ic4bfb98f9df9501b8fc82de2c45db7d7311135ac
Tested: on Linux.
Added convenient vector from array construction for Java.

Change-Id: Ib3fd576cf9fa4b4058a9fd1bbe24a0859bc3917a
Tested: on Linux.
The parser and flatc now allow include directories to be specified.

Bug: 17139854
Change-Id: I0eac65d054951e00a8811ad1d80ba8c37012dbf0
Tested: on Linux.