QoL improvements for data stream handling

[ngjunsiang]

Proposal

Improve quality-of-life (QoL) by adding convenience methods to data-handling classes, and centralise them under a stream module.

Rationale

The interface for DataInputStream and DataOutputStream are inspired by the classes of the same name from Java (see https://docs.oracle.com/javase/8/docs/api/java/io/DataOutputStream.html). Java programmers would no doubt be more familiar with those method names and their uses.

However, their use in a Python package is less helpful, as Python generally does not use these names. Furthermore, IEEE1278.1-2012 also does not use those names, instead using 16-bit signed integer, 8-bit unsigned integer, etc.

Furthermore, a number of issues & PRs can be traced to use of the wrong method:

• Fixed Signal PDU serialization #34
• [fix] read and write unsigned bytes in SignalPdu #57
• VariableDatum object cannot hold negative signed integers #13
• PDU Length is serialized/parsed as a byte when it is a short #64

These bugs can be more easily avoided with names that align with the IEEE1278.1-2012 documentation, and with the type names that already exist in the types module.

Changes

This PR proposes a couple of QoL improvements to make bugs easier to catch and fix, and to lay the ground for further work on type validation. The changes in this PR do not break any existing code.

• Add convenience methods (read_int8(), ... read_uint8(), ..., and the write_* equivalents) to the DataInputStream and DataOutputStream classes. These methods are aliases that call the appropriate read/write method.
• Add a stream module from which to import the DataInputStream and DataOutputStream classes. Unlike in Java, Python does not have a convention of requiring classes to be in separate file. Furthermore, Python prefers lowercase module names. This naming aligns better with PEP8 and other Python conventions expected by Python programmers.

Future work (beyond this PR)

If this PR is approved, future work may include:

• moving DataInputStream.py and DataOutputStream.py under stream altogether, simplifying the directory structure
• gradually switching usage of legacy methods to the convenience methods for clarity
• applying type annotations more consistently to facilitate the use of static checkers to catch type errors before runtime.

[leif81]

Thank-you @ngjunsiang