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

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

man8/thin_rmap.txt

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+NAME
+  thin_rmap - output reverse map of a thin provisioned region of blocks from
+  metadata device or file.
+
+SYNOPSIS
+  thin_rmap [options] {device|file}
+
+DESCRIPTION
+  thin_rmap outputs the reverse mapping stored in the metadata on a device or
+  file between a region of thin provisioned pool blocks and the associated thin
+  provisioned devices.
+
+  This tool cannot be run on live metadata.
+
+OPTIONS
+  -h, --help		Print help and exit.
+  -V, --version		Print version information and exit.
+  --region {block range}	Specify range of blocks on the data device.
+
+    At least one region must be specified.  Multiple regions may be specified.
+
+    The range takes the format <begin>..<one past the end>.  For example,
+    "5..45" specifies data blocks 5 to 44 inclusive, but not 45.
+
+EXAMPLES
+
+  $ thin_rmap --region 5..45 /dev/pool-metadata
+
+DIAGNOSTICS
+  thin_rmap returns an exit code of 0 for success or 1 for error.
+
+SEE ALSO
+  thin_check(8), thin_dump(8), thin_repair(8), thin_restore(8), thin_metadata_size(8)
+
+AUTHOR
+  Joe Thornber <ejt@redhat.com>, Heinz Mauelshagen <HeinzM@RedHat.com>
+