readme: give a more concrete patch example

I think a more concrete example makes it a little easier to grok.
kmod/core: fix kpatch_num_registered decrement

Oops, kpatch_unregister doesn't decrement kpatch_num_registered whenever
it's > 1.
kmod/core: kpatch_unregister return error if !kpmod->enabled

It's probably cleaner to just return -EINVAL if the kpmod isn't enabled,
instead of warning and continuing, which would be dangerous.

I think the reason I had it WARN before is because this condition
shouldn't be possible given the source for the patch module.  But the
core module can't necessarily assume that it's our trustworthy patch
module code on the other side.
Merge pull request #169 from jpoimboe/unregister-fix

kmod/core: fixes in the unregister path
Merge pull request #168 from jpoimboe/readme-patch-example

readme: give a more concrete patch example
kpatch-build: replace special characters in module name

Having a '.' in the kmod name confuses lsmod, which prints "Size" and
"Used by" values of -2.  Prevent any special characters other than '_'
and '-', so that our patch module names will be consistent with typical
kmod names.
Merge pull request #170 from jpoimboe/module-special-chars

kpatch-build: replace special characters in module name
kmod/core: minor style fix

For compatibility with checkpatch
Merge pull request #171 from jpoimboe/style

kmod/core: minor style fix
test: test 'kpatch reload' and cleanup between tests
test: add cmdline-string test
test: fix uninitialized skip variable
test: add meminfo-cmdline test
test: add custom test for kpatch replace
test: make output messages easier to read
test: make .init sections can't be changed
test: fix custom test error condition check
test: send status messages to log file
test: fix unload_all
test: add test for loading multiple modules