Refactor build script

[jprendes]

This PR refactors the wasmedge-sys build script to remove the dependency on the external commands wget, tar and bash.
It also reduces the amount of duplicated code in the build script.

Fixes #30.
Fixes #34.

[juntao]

Hello, I am a code review bot on flows.network. Here are my reviews of code commits in this PR.

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Commit 5d7d6f878ddf0795ab9d2296c04bbc2bc0d362ca

Key Changes:

• Added new dependencies: reqwest, flate2, tar, sha256, lazy_static, phf
• Created new files: build_paths.rs, build_standalone.rs
• Reorganized code structure by moving some code to separate modules
• Improved search for libwasmedge by using a list of search locations

Potential Problems:

• The function find_wasmedge() is now split into two separate functions based on the static feature. This could lead to confusion and potential bugs if not handled correctly.
• The code now relies on external dependencies (reqwest, flate2, tar, sha256, lazy_static, phf). Make sure these dependencies are properly documented and versioned.
• The changes made to the build script may introduce compatibility issues with existing code or build configurations. It is important to thoroughly test the changes in different environments.
• The added search locations are hardcoded. Consider making them configurable or dynamically determined based on the system.
• The patch does not include any information about the reasoning behind the changes or any additional documentation to help understand them. It would be helpful to have more context when reviewing the changes.

[jprendes]

@apepkuss PTAL :-)

[apepkuss]

@jprendes This PR is a BIG STEP for the build script. Really thank you for your efforts. BTW, could this PR also fix #34? In this issue, @ipuustin mentions "proxy prison". Thanks.

[jprendes]

I pushed a new version. To help with reproducible builds:

• It now validates the checksum of the downloaded archives
• Adds env-vars to configure a proxy for the downloads: WASMEDGE_STANDALONE_PROXY{_USER,PASS}.
• Adds an env-var to use a local archive: WASMEDGE_STANDALONE_ARCHIVE

@ipuustin I think this should address the concerns in #34