Improve docstrings of Indicator and LowHigh #1600

Job	Run time
Documentation	12m 15s
Julia lts - macos-latest - x64 - push	11m 31s
Julia lts - windows-latest - x64 - push	9m 50s
Julia lts - ubuntu-latest - x64 - push	7m 45s
Julia 1 - ubuntu-latest - x64 - push	12m 43s
Julia 1 - macos-latest - x64 - push	20m 11s
Julia 1 - windows-latest - x64 - push	14m 17s
	1h 28m 32s

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