Struct accessors and other fun things

[jpsamaroo]

This adds all sorts of great stuff, most of which was necessary to port Brendan Gregg's offwaketime script (shipped in bcc) to Julia.

TODO:

• [x] Add offwaketime to examples/
• [x] Test struct accessors
• [x] Test new Hostmap ctor
• [x] Test RT.get_current_task() and RT.probe_read_kernel
• [x] Test RT.memcpy!
• [x] Test probe object merging
• [x] ~Fix~Skip builds.sr.ht VMLinuxBindings build failure
• [ ] Implement object groups for automatic map merging

[jpsamaroo]

Waiting on https://github.com/JuliaRegistries/General/pull/41725 for VMLinuxBindings.jl

[codecov-commenter]

Codecov Report

Merging #31 (9e3c7a0) into master (0043652) will not change coverage. The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #31    +/-   ##
=======================================
  Coverage    0.00%   0.00%            
=======================================
  Files          18      20     +2     
  Lines         766    1009   +243     
=======================================
- Misses        766    1009   +243     

Impacted Files	Coverage Δ
src/BPFnative.jl	0.00% <ø> (ø)
src/common.jl	0.00% <0.00%> (ø)
src/compiler.jl	0.00% <0.00%> (ø)
src/extra.jl	0.00% <0.00%> (ø)
src/host/kallsyms.jl	0.00% <0.00%> (ø)
src/host/maps.jl	0.00% <0.00%> (ø)
src/libbpf.jl	0.00% <0.00%> (ø)
src/probes.jl	0.00% <0.00%> (ø)
src/runtime/buffers.jl	0.00% <0.00%> (ø)
src/runtime/helpers.jl	0.00% <0.00%> (ø)
... and 5 more

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