[ecc] Support producing standalone executables

[Officeyutong]

Still in draft

Closes #226

This PR cleans up the code of ecc, and add support to produce standalone executable that can run JSON skeleton.

More description to be added.

Note:

• Currently it ONLY supports generate executables that uses bpf-loader. Use the option -s to control whether to generate the executable.
• Other changes are optimizing the code and cleaning it up

[codecov]

Codecov Report

Merging #236 (a0dc55a) into master (87d127f) will decrease coverage by 2.16%.
The diff coverage is 82.93%.

❗ Current head a0dc55a differs from pull request most recent head 42b82c0. Consider uploading reports for the commit 42b82c0 to get more accurate results

@@            Coverage Diff             @@
##           master     #236      +/-   ##
==========================================
- Coverage   75.61%   73.45%   -2.16%     
==========================================
  Files           8       14       +6     
  Lines        1718     1733      +15     
==========================================
- Hits         1299     1273      -26     
- Misses        419      460      +41     

Impacted Files	Coverage Δ
compiler/cmd/build.rs	95.14% <ø> (ø)
compiler/cmd/src/bpf_compiler/standalone.rs	0.00% <0.00%> (ø)
compiler/cmd/src/main.rs	11.11% <0.00%> (-3.18%)	⬇️
compiler/cmd/src/wasm.rs	0.00% <0.00%> (ø)
compiler/cmd/src/helper.rs	56.00% <56.00%> (ø)
compiler/cmd/src/config/options.rs	72.30% <72.30%> (ø)
compiler/cmd/src/config/mod.rs	81.76% <81.76%> (ø)
compiler/cmd/src/export_types.rs	96.82% <90.90%> (+1.17%)	⬆️
compiler/cmd/src/bpf_compiler/mod.rs	92.13% <92.13%> (ø)
compiler/cmd/src/bpf_compiler/tests.rs	100.00% <100.00%> (ø)
... and 3 more

[yunwei37]

remember to add license header for the new files.

[Officeyutong]

remember to add license header for the new files.

Do we need license headers for the template C source? I think it's not ecessary, because it's used for code generating

[yunwei37]

yes，not necessary for them.