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

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

man8/thin_check.txt

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+NAME
+  thin_check - validates thin provisioning metadata on a device or file
+
+SYNOPSIS
+  thin_check [options] {device|file}
+
+DESCRIPTION
+  thin_check checks thin provisioning metadata created by the device-mapper
+  thin provisioning target on a device or file.
+
+  The 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-mappings	Skip checking of the block mappings which make up the bulk of the metadata.
+
+  --ignore-non-fatal-errors	Will only return a non-zero exit code if it finds a fatal error.
+
+    An example of a nonfatal error is an incorrect data block reference count
+    causing a block to be considered allocated when it in fact isn't.  Ignoring
+    errors for a long time is not advised, you really should be using
+    thin_repair to fix them.
+
+EXAMPLE
+  Analyses thin provisioning metadata on logical volume /dev/vg/metadata:
+
+    $ thin_check /dev/vg/metadata
+
+  The device must not be actively used by the target when running.
+
+DIAGNOSTICS
+  thin_check returns an exit code of 0 for success or 1 for error.
+
+SEE ALSO
+  thin_dump(8), thin_repair(8), thin_restore(8), thin_rmap(8), thin_metadata_size(8)
+
+AUTHOR
+  Joe Thornber <ejt@redhat.com>, Heinz Mauelshagen <heinzm@redhat.com>
+