improve code coverage, found and fixed a few bugs

[jeking3]

Got parser up to 99.7% code coverage, a significant improvement. Found three issues along the way:

1. Using %1$T in "don't throw" mode would throw an unhandled exception.
2. The parser allowed for a number to follow an asterisk, for example %1$*4.*5d.
3. The examples were not actually executed to verify they are successful.

Apologies for the whitespace cleanup applied by my editor (geany).

[codecov]

Codecov Report

Merging #53 into develop will increase coverage by 8.21%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           develop      #53      +/-   ##
===========================================
+ Coverage    79.59%   87.81%   +8.21%     
===========================================
  Files           10       10              
  Lines          799      886      +87     
===========================================
+ Hits           636      778     +142     
+ Misses         163      108      -55

Impacted Files	Coverage Δ
include/boost/format/parsing.hpp	97.3% <100%> (+14.52%)	⬆️
include/boost/format/format_class.hpp	100% <0%> (ø)	⬆️
include/boost/format/group.hpp	100% <0%> (ø)	⬆️
include/boost/format/alt_sstream.hpp	100% <0%> (ø)	⬆️
include/boost/format/alt_sstream_impl.hpp	42.64% <0%> (+0.71%)	⬆️
include/boost/format/feed_args.hpp	96.74% <0%> (+0.81%)	⬆️
include/boost/format/format_implementation.hpp	92.41% <0%> (+1.67%)	⬆️
include/boost/format/internals.hpp	89.47% <0%> (+5.75%)	⬆️
include/boost/format/free_funcs.hpp	94.11% <0%> (+17.64%)	⬆️
... and 1 more

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