added this textbook pointer

- Igor R. Shafarevich, Alexey O. Remizov:
*Linear Algebra and Geometry*(2012) [doi:10.1007/978-3-642-30994-6, MAA-review]

here and in a bunch of related entries which were mostly lacking any basic references (such as *matrix* etc.)

added pointer to

- Daniel Murfet,
*Logic and linear algebra: an introduction*[arXiv:1407.2650]

(here and in some related articles, such as at *FinDimVect*)

added pointer to:

- Sheldon Axler,
*Linear Algebra Done Right*, Springer (2015) [doi:10.1007/978-3-319-11080-6]

just noticed that in many entries the floating context menu for Linear Algebra has accidentally been replaced by that for Homotopy Theory (evidently a mistake propagated by copy-and-pasting, I guess this is all my fault). Am fixing this now, as far as I can spot occurrences.

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