Log all but string and char as hex

[Christian-B]

Do not merge until SpiNNakerManchester/SpiNNakerGraphFrontEnd#125 is Green!

Note: @oliverrhodes and @lplana would be against the complete removal of the ability to print values directly to iobuf during debugging. He is mainly interested in ints and accums. He does not mind if the abilty to format these values is removed.

I would not recommend merging this until.

1. We have a matching PR on spin tools which shows a clear saving in ITCM
2. We have the single dict file implemented

[lplana]

As I mentioned to @Christian-B and @dkfellows, I don't think that there is a need to get rid of 'io_printf()' and the ability to print values directly to 'IO_BUF'. 'io_printf()' is quite stable and requires little or no maintenance.

If we got it right (big if), the linker will not link in any function that is not called, thus 'io_printf()' will not be a part of the executable file if it is not used in the application. The user can choose to use it or not, depending on their needs and the size of their executable.

The case may be that the 'logging' infrastructure uses 'io_printf()'. In this case, 'logging' should stop using 'io_printf()' and use a 'hex-based' trimmed-down version, as implemented in this pull request. In this case, 'io_printf()' would not be linked in and the executable would actually benefit from the size reduction, but users like me would still have the option of using 'io_printf()' and read 'IO_BUF' directly, without the need to consult the dictionary.

[coveralls]

Pull Request Test Coverage Report for Build 924

• 34 of 46 (73.91%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.3%) to 92.229%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
spinn_utilities/make_tools/replacer.py	24	36	66.67%

Files with Coverage Reduction	New Missed Lines	%
spinn_utilities/make_tools/replacer.py	1	80.82%

Totals
Change from base Build 922:	0.3%
Covered Lines:	4890
Relevant Lines:	5302

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💛 - Coveralls