ISO 15919 strict nasalization option

[bwasty]

Quote from https://en.wikipedia.org/wiki/ISO_15919#Comparison_with_UNRSGN_and_IAST:

ISO 15919 has two options about anusvāra. (1) In the simplified nasalization option, an anusvāra is always transliterated as ṁ. (2) In the strict nasalization option, anusvāra before a class consonant is transliterated as the class nasal—ṅ before k, kh, g, gh, ṅ; ñ before c, ch, j, jh, ñ; ṇ before ṭ, ṭh, ḍ, ḍh, ṇ; n before t, th, d, dh, n; m before p, ph, b, bh, m.

It would be nice to support the strict option I think.

[vvasuki]

Basically involves porting https://github.com/indic-transliteration/indic_transliteration_py/blob/d8f9815abee59b438ff139488440807f27cd88aa/indic_transliteration/sanscript/schemes/__init__.py#L44 here.