New feature: with-friction

[cormacanderson]

This is applicable to vowels, consonants, and clicks. On vowels:

• [ ] i͓ with-friction unrounded close front vowel
• [ ] u͓ with-friction rounded close back vowel
• [ ] ɯ͓ with-friction unrounded close back vowel

On consonants:

• [ ] r͓ with-friction voiced alveolar trill consonant
• [ ] ɭ͓ with-friction voiced retroflex lateral approximant consonant
• [ ] ʟ͓ with-friction voiced velar lateral approximant consonant

On clicks:

• [ ] ǀ͓ with-friction voiceless dental click consonant
• [ ] ǁ͓ with-friction voiceless lateral click consonant
• [ ] ǂ͓ with-friction voiceless palatal click consonant
• [ ] ǃ͓ with-friction voiceless alveolar click consonant

cf. http://phoible.github.io/conventions/

[tresoldi]

It currently applies only to vowels, but I support extending it to consonants as well.

[LinguList]

Can we use this as an alternative feature for vowels? I don't want to include new features, but feature values are okay. Consider whistled sibilants: I added "sibilancy:whistled-sibilant".

[cormacanderson]

For vowels it's already in as a feature, frication: with-frication (simply friction would be better). For consonants it's a bit tricky to know where it would go. The articulation feature perhaps?

[LinguList]

I think, this could work, so we go for articulation = strong or none to articulation = strong or with-friction or none now.The order should also be okay for the grapheme then.