unknown symbols

Looking at the contents of Latin Extended Additional, I realised that
there were a lot of characters I didn't know. A bit of googling showed
that no-one else seems to know them either! Can anyone here explain the
uses of the following?

ḁ (a ring below) ḉ (c cedilla acute) ḡ (g macron) ḣ (h dot above)
ḧ (h dieresis) ḩ (h cedilla) ḿ (m acute) ṕ (p acute)
ṥ (s acute & dot above) ṧ (s caron & dot above) ṩ (s dot above & below)
ṳ (u dieresis below) ṽ (v tilde) ṿ (V dot below) ẙ (y ring over)

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