Adding alias to exprs_values argument

[antagomir]

The scater package has added deprecation message on the exprs_values argument and replaced this with assay_name as the argument to choose the assay for plotting SE objects. See scater PR #187. Also the mia family of packages (for microbiome analysis) are using the assay_name argument.

The assay_name refers more explicitly to assays than exprs_values.

I suggest to make the same change in the scuttle package. We can prepare a PR if this suggestion is supported: deprecate exprs_values, replace it with assay_name, and use former as an alias for the latter.

[LTLA]

exprs_values (and all other underscore arguments in scuttle) is soft-deprecated, as I prefer to use:

• dots as separators in argument names
• lower camel case in function names
• upper camel case in class names
• underscores in internal function names

Right now, I only keep the underscore'd arguments around to avoid breaking existing code, owing to the history of some of the scuttle functions that were ported from and then re-exported in scater. It would not be desirable to transition from one underscore'd argument to another when I want people to use the dot arguments (assay.type).

[alanocallaghan]

Small correction, exprs_values isn't deprecated

[antagomir]

The mia* and scater packages have switched to using assay.type now.