[manpages] Rewrite man pages in a simpler text format.

Makefile still needs work, but I wanted to commit to save progress.

man8/cache_check.txt

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+NAME
+  cache_check - validates cache metadata on a device or file.
+
+SYNOPSIS
+  cache_check [options] {device|file}
+
+DESCRIPTION
+  cache_check checks cache metadata created by the device-mapper cache target
+  on a device or file.
+
+  This tool cannot be run on live metadata.
+
+OPTIONS
+  -q, --quiet	Suppress output messages, return only exit code.
+  -h, --help	Print help and exit.
+  -V, --version	Output version information and exit.
+  --super-block-only	Only check the superblock.
+  --skip-hints		Skip checking of the policy hint values metadata.
+  --skip-discards	Skip checking of the discard bits in the metadata.
+  --clear-needs-check-flag	Clears the 'needs_check' flag in the superblock.
+
+    The kernel may set a flag to force the pool to be checked before it's next
+    activated.  Set this switch to clear the flag if the check is successful.
+
+EXAMPLE
+  Analyses and repairs cache metadata on logical volume /dev/vg/metadata:
+
+    $ cache_check /dev/vg/metadata
+
+  The device may not be actively used by the target when running.
+
+DIAGNOSTICS
+  cache_check returns an exit code of 0 for success or 1 for error.
+
+SEE ALSO
+  cache_dump(8), cache_repair(8), cache_restore(8)
+
+AUTHOR
+  Joe Thornber <ejt@redhat.com>, Heinz Mauelshagen <HeinzM@RedHat.com>
+