Fix #22, solve on [=] key if the input is not a variable name.

If the input is a variable name, this would be an assignment
so the "=" sign is inserted.
Otherwise, the equation is solved which makes usage much more
comfortable in certain keyboards like mine.
5 jobs for master in 19 minutes and 3 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #494582
build:fedora

00:03:40

passed #494584
allowed to fail
build:snap

00:16:11

passed #494583
build:ubuntu

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  Test
passed #494586
test:fedora

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passed #494585
test:ubuntu

00:02:47