Misc doc changes

[kianmeng]

List of changes:

• Fix image not showing in HTML page
• Use common source url
• Fix invalid SPDX license id
• Update license section
• Set and use latest ex_doc
• Fix markdown in changelog
• Badges and more badges!
• Fix typos
• Update gitignore
• Update formatter config
• Remove extra spaces
• Add logo

Screenshot:

[coveralls]

Pull Request Test Coverage Report for Build 8f1992241c0ea936ff6ac225683c3df536df6aee-PR-476

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 86.464%

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Totals
Change from base Build 24997fb649d778f654c1adad0006f7ad529a1184:	0.3%
Covered Lines:	313
Relevant Lines:	362

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 8f1992241c0ea936ff6ac225683c3df536df6aee-PR-476

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage remained the same at 86.188%

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Files with Coverage Reduction	New Missed Lines	%
lib/quantum/executor.ex	2	91.43%
<!--	Total:	2		-->

Totals
Change from base Build 24997fb649d778f654c1adad0006f7ad529a1184:	0.0%
Covered Lines:	312
Relevant Lines:	362

---

💛 - Coveralls

[c-rack]

Thanks!