Revert most of c1374ba032a06510e741f0944547dfeb655edadd

Commit c1374ba032a06510e741f0944547dfeb655edadd for some reason reverted
commits 4a44369d8ab01feb69bee0875d659fe7bd086970 and
91cbc9aff14c6290071e6d317024cd4ebf24917d.
eras_list initial commit
add eras_list and wesnoth.get_era
update changelog
wmllint: Fix incorrect ToD schedule image substitution
wmllint: Add check for deprecated [theme] name= usage
wmllint: Add check for user-visible [theme]s without a name or description
wmllint: Add check for [theme]s without an id
wmllint: Spellcheck [terrain_type] editor_name= and help_topic_text=
Add wmllint spelling exception for 'unwalkable'
Fix typo: 'facilites' -> 'facilities'
'rarified' -> 'rarefied'
EI S8: Disable spellchecking for a single line
HttT: Prevent wmllint from complaining about UK spelling in a WML comment
THoT S12: Move a couple of macros down to appease wmllint's [message] id check
wmllint: Implement [terrain_type] aliasof conversion for changes in 1.11.[89]

Adds a text transform step for the aliasof attribute under
[terrain_type] accounting for several changes to base terrain aliasing
in Wesnoth 1.11.8 and 1.11.9, including:

 * 10854d4802c4953cf05a8e28cb81ba5ab8d52b29 and related commits
 * c25849b7ea0a18e32d9065cfca91e703e179cf04 (Vit -> Vt in 1.11.9)

Just like usual terrain string conversions, this step can be disabled
for a specific line using # wmllint: noconvert.
wmllint: Add a small comment block

This is documentation for e1852e6854875f9d920f7f1862350f87afa854ab.
wmllint: Ignore Mercurial .hg directories
wmllint: Extend [terrain_type] aliasof conversion to mvt_alias
wmllint: Extend [terrain_type] aliasof conversion to def_alias