fix grammar/typo in build docs

There was a word missing.

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extra : transplant_source : %B2%3E%E6%8CF%00%89%0E%AF%3A%C2%40%1E%D9%A7%E7S%E67A
Set correct baseclass for heap allocated type subclasses.

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extra : transplant_source : E%BEhL%948%C1%07%EC%BDx%7C%7E%C2%3Fq%1D%EFE%BC
Fix typo

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extra : transplant_source : %A3%7E%9BWre%B4%86%A0%E5%B2Kk%B9%DEf%3F%FD3%0E
Clarify cdef vs. def function arguments.

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extra : transplant_source : %86.-%DA%5C%B1%CE%B8%40%BD%BA%E2%F0%B6f%C40%EB%B0%08
minor doc fixes

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extra : transplant_source : %9E%DF%DFQ%18h%9D%1Ax%FAV%1F%28%E8%86%E4%91%21%EF%26
merge 0.19.x branch into master