Inherit common SSplot Parameters

[efletcherPIFSC]

Created generic functions SSplotGeneric , SSplotGenericLegend, SSplotGenericPar, SSplotGenericUncertianty to re-use common parameter documentation that ss3diags SSplot functions, via use roxygen tag@inheritParams. Resolves #2.

Implementation of SSplotGenericPar resolves #66.

In addition:

• Included markdown notation to SSplot roxygen code documentation
• Added links to other functions such as r4ss::SS_Summarize, and replaced "TRUE/FALSE" with link to base::Logical
• Values in subplots, indexfleets, and punits are listed in a bulleted list
• Typo fixes

[efletcherPIFSC]

@MOshima-PIFSC Is the item description listed in the subplots parameter accurate for:

• SSPlotModelComp
• SSplotEnsemble
• SSplotHCxval
• SSplotJABBAres
• SSplotRetro
• SSplotRunsTest

[efletcherPIFSC]

@MOshima-PIFSC Didn't resolve any git code conflicts. Hence the dirty git conflict code. Fixing that.