lower-cases atbash-cipher alphabet encoded example

This matches the behavior of the Ruby implementation.

[#663]
removes code from atbash-cipher.md

[#663]
removes code from binary and rewrites description of binary system

[#663]
rewrites crypto-square assignment to remove Ruby code

[#663]
rewrites etl assignment to avoid Ruby code

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removes Ruby code from grade-school assignment

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removes Ruby code from matrix.yml and corrects columns

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removes Ruby code from kindergarten-garden

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renames kindergarden-garden to kindergarten-garden to correct spelling

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removes Ruby code from allergies assignment

[#663]
rewrites accumulate to eliminate Ruby-specific-ness

[#663]
removes Ruby from phone-number assignment

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removes Ruby from prime-factors assignment

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removes Ruby from queen-attack assignment

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removes Ruby from raindrops assignment

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removes Ruby code from robot-simulator assignment text

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removes Ruby code from saddle-points assignment text

[#663]
removes Ruby code from say assignment text

[#663]
removes Ruby code from scrabble-score assignment text

[#663]
removes Ruby code from series assignment text

[#663]