[fkjellberg]

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Remove the package private BitStream class, which only ExplodingInputStream used, and use BitInputStream directly instead.

API change

• Adds BitInputStream.readByte() to the public API. It reads the next 8 bits from the stream and returns them as an int in range 0 to 255. It replaces BitStream.nextByte().

Other changes

• BZip2CompressorInputStream and ExplodingInputStream call readByte() instead of readBits(8) or nextByte().
• BitStream.nextBits(int) is removed and its caller uses readBits(int) instead. nextBits threw an exception when asked for more than 8 bits. Its only caller asks for 6 or 7 bits, depending on the dictionary size, so the check was never triggered.
• Added tests for the new method in BitInputStreamTest.