(feature) Add hard backspace option

[HarryHighPants]

Problem:
When in insert mode some users would like to keep the spacing of the line untouched while backspacing characters.

Feature request issue:
#42

Proposed Solution:

• Add a hard backspace option which replaces backspaced text with spaces
• This option can be enabled in the extensions settings

Demo:

[jkyeung]

Love the idea. Not so crazy about the name. To me, there's nothing "soft" about the regular Backspace, so "hard" makes no sense to me. If anything, the regular Backspace strikes me as the "harder" one.

So what name would I like instead? Good question. Off the top of my head, I don't have a good, self-documenting alternative that is concise or pretty. I would err on the side of verbose-but-descriptive, like maybe overtype.preservePositioningOnBackspace.

Or I might choose to punt and just have the setting be called overtype.backspaceMode, and have either numeric choices, or fixed strings like "default" and "position-preserving". (This has the potential advantage of accommodating more than 2 defined behaviors, as I laid out in my comment on issue #20.)