fix typos

[spaette]

docs/src/eigenproblems/power_method.md docs/src/linear_systems/bicgstabl.md src/history.jl

I used CamelCase in the following comment.

$ ed -s IterativeSolvers.jl/src/history.jl <<<'175,176p'
# If PartialHistory, there's no need to store a vector or matrix, instead
# store nothing or store a vector respectively.
$ 

[coveralls]

Pull Request Test Coverage Report for Build 4930271493

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.331%

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Totals
Change from base Build 4540511022:	0.0%
Covered Lines:	1933
Relevant Lines:	1986

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💛 - Coveralls