Document some internal macros and other small improvements

[Mingun]

1. First, fixed all references to the XML standard to point to the version 1.1 of the standard.
2. Second, document internal macros that performs reading.
3. The last, add a quick reference to the deserializer module from the introduction page. I noticed, I often need it.

[codecov-commenter]

Codecov Report

Merging #577 (0c394c6) into master (f822669) will increase coverage by 0.03%.
The diff coverage is 95.65%.

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@@            Coverage Diff             @@
##           master     #577      +/-   ##
==========================================
+ Coverage   64.24%   64.27%   +0.03%     
==========================================
  Files          34       34              
  Lines       16618    16624       +6     
==========================================
+ Hits        10676    10685       +9     
+ Misses       5942     5939       -3     

Flag	Coverage Δ
unittests	64.27% <95.65%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/de/key.rs	93.83% <ø> (ø)
src/de/simple_type.rs	93.86% <ø> (ø)
src/errors.rs	11.11% <ø> (ø)
src/name.rs	87.82% <ø> (ø)
src/reader/mod.rs	94.93% <ø> (ø)
src/reader/slice_reader.rs	100.00% <ø> (ø)
src/se/key.rs	96.79% <ø> (ø)
src/se/mod.rs	92.11% <ø> (ø)
src/lib.rs	20.17% <80.00%> (+0.06%)	⬆️
src/de/mod.rs	69.67% <100.00%> (ø)
... and 2 more

... and 1 file with indirect coverage changes

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