Still on my offset-text rewrite spree...

Currently, the formatter API (in charge of picking the strings for the tick labels, axis offset and cursor position in the status bar) is a bit messy: the public methods available are

• Formatter.__call__(self, val, idx): computes the label texts
• Formatter.format_data(self, val): not publicly used
• Formatter.format_data_short(self, val): computes the cursor position text
• Formatter.get_offset(self): returns the offset text
• Formatter.set_locs(self, locs): required for computing the labels
• Formatter.fix_minus(self, s): overriden only by ScalarFormatter to use a unicode minus

FixedFormatter also provides set_offset_string.

The commonly used ScalarFormatter and LogFormatter also provide pprint_val (with different signatures, and not publicly used).

ScalarFormatter also provides a couple of getter/setters (for useOffset, useLocale, scientific, powerlimits); LogFormatter provides base and label_minor as setters for instance variables.

LogFormatterExponent and LogFormatterMathtext are variants of LogFormatter.

EngFormatter also provides format_eng (not publicly used).

There are also a bunch of instance attributes which are public but probably intended as private.

I propose simplifying the API to the following:

• Formatter.get_label_text(self, val: float, idx: int): computes the label texts
• Formatter.get_cursor_text(self, val: float): computes the cursor position text
• Formatter.get_offset_text(self) and Formatter.set_offset_text(self, s: str): get/set the offset text
• Formatter.set_locs(self, locs: array-like): because we need it
• Formatter.set_uselocale(self, b: bool): because there's no reason only ScalarFormatter has it

(the new method names can be made to fallback on the old method names with a deprecation warning in the base class)

and drop or make private basically everything else:

• fix_minus (let's first check if any backend doesn't support unicode)
• pprint_val/format_eng
• the various instance attributes which should have been private to start with (keeping: scientific, powerlimits, base, label_minor, using getter/setters)

and fold the LogFormatterExponent and LogFormatterMathText classes into options for the LogFormatter class.

Thoughts?