CI: deploy wasm

[ChinYikMing]

Since wasm is deployed on Github Pages, thus it is reasonable to use CI to deploy automatically.

The CI supports two events: merged pull request and workflow_dispatch. The former only run after merging and latter is used to deploy by maintainer manually. It also verifies whether any associated files have changed. If so, carry out the CI; if not, stop.

Related: #75

[ChinYikMing]

Please merge PR #388 first before merging this PR.

[ChinYikMing]

Before merging this PR, please do the following to make the CI having permission:

1. Generate a PAT with read and write permission (Settings --> Developer Settings --> Personal Access Tokens --> Tokens(classic) --> Generate New Tokens(classic))
2. Store it in rv32emu's settings --> Secret and variables --> Actions --> Add a secret, and name it as RV32EMU_DEMO_TOKEN, the value is PAT which generated by previous step

[ChinYikMing]

After merging this PR, please run the CI manually for the first time using workflow_dispatch event. Then, we should see the wasm deployed on rv32emu-demo

[jserv]

generate a PAT with read and write permission

Please indicate the minimal requirements for the scopes of the access for personal tokens such as write:package

[ChinYikMing]

generate a PAT with read and write permission

Please indicate the minimal requirements for the scopes of the access for personal tokens such as write:package

Please select the permissions write:packages and read:packages(under write:packages).