Add copyright headers

[odow]

x-ref jump-dev/AmplNLWriter.jl#155

[codecov]

Codecov Report

Merging #134 (c0d54e8) into master (6a6ebbf) will decrease coverage by 4.93%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #134      +/-   ##
==========================================
- Coverage   59.18%   54.25%   -4.94%     
==========================================
  Files           4        4              
  Lines         713      717       +4     
==========================================
- Hits          422      389      -33     
- Misses        291      328      +37     

Impacted Files	Coverage Δ
src/Clp.jl	71.42% <ø> (ø)
src/MOI_wrapper/MOI_wrapper.jl	82.79% <ø> (-8.36%)	⬇️
src/libClp.jl	28.08% <ø> (-2.25%)	⬇️
src/precompile.jl	0.00% <ø> (ø)

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