popm/wasm: improve and tidy up Go code

[joshuasing]

Summary
Initial pass to improve and tidy up the Go code for the WASM PoP Miner.
This is the first of many pull requests to improve the WASM and create a TypeScript (NPM) package that can be used to run the PoP Miner.

Changes
This splits the web/popminer/popminer.go file into 6 files:

• api.go: Contains all API types
• dispatch.go: Contains all methods that can be dispatched from JS.
  The majority of the code in this file was moved from popminer.go.
• network.go: Contains Hemi/Bitcoin network settings
• network_local.go: Contains localnet settings (behind build tag, build with -tags "hemi_localnet" to enable)
• popminer.go: Contains the main function and core
• util.go: Contains utility functions for working with JS.

This contains a lot of miscellaneous improvements, however the notable ones are:

• Invoke Promise resolve function with js.Value instead of marshalled JSON, meaning that the result can be used directly without the need to encode/decode JSON.

• Make all errors use a common object (created by the jsError function) that contains the error message, a timestamp, and the debug stack, allowing for easier debugging.

• Replace wasmPing method with version - wasmPing is not very useful and was only used for testing the connection between JS and WASM. version returns useful version information and allows the same testing.

• Use structs for all return types. The jsValueOf function supports converting structs to JavaScript Objects via reflection.

• Move network configurations into a separate file and use constants. I think this is cleaner than the previous solution, and allows localnet to only be available when built with the 'hemi_localnet' build tag. Note: I have found the networks to be slightly confusing, as we need to interact with Hemi and Bitcoin. This "standardises" the networks in the WASM PoP miner and uses the Hemi network name, not the Bitcoin network name. If this is not useful, then this can be reverted.

• Move dispatch function to under a global object to prevent collisions and other issues. - The dispatch function is now placed in a @hemilabs/pop-miner global object. An example of accessing the dispatch function would be globalThis['@hemilabs/pop-miner'].dispatch(args). The name @hemilabs/pop-miner is used, as it will be the name of the NPM package.

Other miscellaneous changes:

• Fix typo in cmd/popmd/popmd.go
• Added versioning to and cleaned up web/Makefile
• Reorganised code
• Changed default logging level to WARN and added ability to change log level with linker flag (e.g. -X main.logLevel=TRACE)
• Renamed runpopminer to startPoPMiner
• Use chan struct{} instead of chan bool to block application exit
• Consistently use lowerCamelCase for method names
• Improve some variable and function naming

Please ask any questions and provide any feedback you have.
Note: The wasm_exec.js file is from Go. I added it to Git due to build issues I was having with certain environments, and it allows us to update the file when we want instead of it being whatever is included the user's installed Go version.

The next pull request will contain the initial TypeScript types and their documentation.

[jcvernaleo]

All looks pretty reasonable to me.

OK

[marcopeereboom]

I am overall ok with this but would like to understand why returning a map is preferable over predefined structures.

[marcopeereboom]

I do really want some sort of detection for wasm_exec.js being out of date with the version that lives in the repo. I am even ok with storing the wasm_exec.js version in the repo and comparing it agains the build machine version. But we need some non-human detection of that file's content.