Implement Error trait

[tmfink]

Fixes #141

Introduces a breaking change with the std feature

[codecov]

Codecov Report

Merging #142 (1160765) into master (8c17287) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

❗ Current head 1160765 differs from pull request most recent head 18c1aab. Consider uploading reports for the commit 18c1aab to get more accurate results

@@            Coverage Diff             @@
##           master     #142      +/-   ##
==========================================
- Coverage   93.98%   93.96%   -0.03%     
==========================================
  Files          21       22       +1     
  Lines        2678     2733      +55     
  Branches     2637     2687      +50     
==========================================
+ Hits         2517     2568      +51     
- Misses        161      165       +4     

Impacted Files	Coverage Δ
capstone-rs/src/arch/mod.rs	92.79% <ø> (+1.04%)	⬆️
capstone-rs/src/error.rs	59.52% <ø> (ø)
capstone-rs/src/ffi.rs	100.00% <ø> (ø)
capstone-rs/src/lib.rs	100.00% <ø> (ø)
capstone-rs/src/capstone.rs	92.36% <100.00%> (-1.93%)	⬇️
capstone-rs/src/instruction.rs	92.50% <100.00%> (-1.42%)	⬇️

... and 8 files with indirect coverage changes

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