doc: changelog.md updates

[Totktonada]

• Fixed a typo in a link anchor.
• Added an alternative process (to better highlight why we stick with our one).

[coveralls]

Coverage increased (+0.002%) to 84.215% when pulling 70fdac3 on Totktonada/fix-a-link-in-changelogs-md-notest into b0431cf on master.

[igormunkin]

@Totktonada, thanks for the changes! LGTM since they are trivial.

Side note: I believe we can fix errors and typos, when building the final version of the changelog at the moment git tag is set, but yes, our approach is more flexible and convenient (at least for me).

[Totktonada]

• Renamed 'Alternatives' to 'Alternatives considered'.
• Added the explicit list of considered alternatives (reasons 'why not' are still in the 'Reasoning' section).
• Highlighted the problems we would have without ability to modify a changelog entry at any time (the scenario is suggested by @kyukhin).
• In the commit message:
  • Replaced 'a possible alternative' with 'a declined alternative'.
  • Added 'that' for grammar.
• Rebased on current master.