docs: bad help tags

[tmillr]

doc/gt_changelog.txt

35:or by using the *:colorscheme* vim command.
96:hiding elements has been moved to the *options* table.
112:The configuration for defining styles has been migrated to *options.styles*.
113:As part of this migration, *msg_area_style* has been removed.
133:Additionally, the currently used colorscheme palettes within the *palette*

For example, *:colorscheme* should be |:colorscheme|. Currently, :h :colorscheme takes you to this plugin's docs because of this tag.

The others need to either have a unique prefix, or also be converted into such |TAG| references. E.g. *palette* should probably be |github-nvim-theme-palette|.

---

Also need to change all occurrences of |github-nvim-theme-compile_path| to |github-nvim-theme-options.compile_path|. I stumbled upon this broken reference, not sure if there's any others.

@ful1e5