add configure option for building examples optionally

[pkovacs]

Adding a configure option to build examples optionally. To be consistent with the cmake version, the default is yes.

# turn off building examples
./configure --without-examples ...

[codecov-commenter]

Codecov Report

Merging #149 (2404b9a) into master (cee2886) will decrease coverage by 0.50%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #149      +/-   ##
==========================================
- Coverage   95.25%   94.74%   -0.51%     
==========================================
  Files           3        3              
  Lines         906      971      +65     
==========================================
+ Hits          863      920      +57     
- Misses         43       51       +8     

Impacted Files	Coverage Δ
libjwt/jwt.c	93.28% <0.00%> (-0.71%)	⬇️
libjwt/jwt-openssl.c	98.20% <0.00%> (+0.12%)	⬆️

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[pkovacs]

Resynced my commits to the tip of your new master to allow for fast forward