Documentation and discoverability of additional algorithms

[bbqsrc]

We have two algorithms at play in divvunspell that don't exist in hfst-ospell:

• Case handling
• Penalty weighting for first letter different, last letter difference and Damerau–Levenshtein distance for middle letters

Things to do to make this good:

• Document somewhere sane how the algorithms behave
• Add some information to --help either with a link or with the information itself
• In the suggestion output for divvunspell, show the penalties, and the unmodified weights, as well as the modified weights
• Document how to add the weight information to BHFST files so it can be controlled by the linguist
• If possible, add a flag for disabling the penalty weighting algorithm (like --no-case-handling already does somewhat, but separate the two into different flags)

[nlhowell]

Just a ping: this is important for me; I have orthographic corrections that
specifically apply to the beginning and ends of words; these are given low (or
even zero!) weight.

hfst-ospell makes the correct suggestions, but divvunspell overrides some of
these with much less appropriate corrections. It would be great if I could add
some information to the .bhfst to modify this.

Here's an example.

Input: кера (final glyph is "cyrillic a")
Correct spelling: кера̄ (final glyph is "cyrillic a" + "combining macron")

Suggested spellings (hfst-ospell):

$ echo 'кера' | hfst-ospell tsez.zhfst -S | head
"кера" is NOT in the lexicon:
Corrections for "кера":
кера̄    1.000000
кека    10.000000
кекра    10.000000
кеза    10.000000
кура    10.000000
кераз    10.000000
кеца    10.000000
кецра    10.000000

Suggested spellings (divvunspell):

$ echo 'кера' | divvunspell -b ddo.bhfst -s | head
Reading from stdin...
Input: кера		[INCORRECT]
кеза		15
кека		15
кекра		15
кеца		15
кецра		15
кура		15
кера̄		16
кераз		25
керо		25