Small improvements

[alburezg]

HIGH PRIORITY (BEFORE CRAN)

• Convert demokin_codes from function to object. Update kin names to include female and male relatives (save them in separate columns 'label_female', 'label_male'. Include "sisters", "cousins", etc (irrespective of whether they are older or younger).
• Remove argument consolidate_relatives from rename_kin function. It's not very useful. Also, see next suggestion:
• Allow kin* functions to take "s", "c", "a", "n" as options in kin_output argument without specifying whether they are through older or younger sister
• Update Readme to remove typos and add new kinship diagram
• Remove HMDHFD dependencies?
• Update kin_multi_stage so that default of the argument parity is F.
• Let multistate function return results by state of Focal in addition to state of kin
• Improve error message when f does not have column names and is passed to kin function. The first error message can be "Make sure that p and f are matrices and have the same column names." and the second: "The years given as column names in the p and f matrices must be equally spaced."
• clarify timing of deaths

AFTER CRAN UPDATE

• plot_diagram doesn't work with "s", "c", "a", "n" : maybe give error message saying that it is not possible to create plot unless ALL the relevant kin types are given?

LOW PRIORITY (BEFORE CRAN?)

• In kin* functions, add argument output_age_focal
• In kin*(time_invariant==F), add argument sex_ratio`

AFTER CRAN

• Create package website
• Add an argument kin_summary to kin functions to determine whether a kin_summary should be created or not.
• Improve bar progress