[block_quote] fix nested math in blockquote context

[mmcky]

This PR fixes nested math in block_quotes

It can now parse block quotes such as

Let's listen to Wald longer:

    As a basis for choosing among critical regions the following
    considerations have been advanced by Neyman and Pearson: In accepting
    or rejecting :math:`H_0` we may commit errors of two kinds. We commit
    an error of the first kind if we reject :math:`H_0` when it is true;
    we commit an error of the second kind if we accept :math:`H_0` when
    :math:`H_1` is true. 

without adding > syntax to internal math components.

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  Misses            ?      134           
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[mmcky]

This isn't the perfect solution but it works. In the future should write a block_quote accumulator to support better nestedness

[mmcky]

• [x] cross-checked against example project lecture-python-programming as a test case.