Make the readme use Markdown.

Also get rid of the Japanese readme - I won't be able to maintain that.

README.md

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+# Ruby/ProgressBar: A Text Progress Bar Library for Ruby
+
+Ruby/ProgressBar is a text progress bar library for Ruby.
+It can indicate progress with percentage, a progress bar,
+and estimated remaining time.
+
+## Examples
+
+    % irb --simple-prompt -r progressbar
+    >> pbar = ProgressBar.new("test", 100)
+    => (ProgressBar: 0/100)
+    >> 100.times {sleep(0.1); pbar.inc}; pbar.finish
+    test:          100% |oooooooooooooooooooooooooooooooooooooooo| Time: 00:00:10
+    => nil
+
+    >> pbar = ProgressBar.new("test", 100)
+    => (ProgressBar: 0/100)
+    >> (1..100).each{|x| sleep(0.1); pbar.set(x)}; pbar.finish
+    test:           67% |oooooooooooooooooooooooooo              | ETA:  00:00:03
+
+## API
+
+- `ProgressBar#new(title, total, out = STDERR)`
+
+  Display the initial progress bar and return a
+  ProgressBar object.  _title_ specifies the title,
+  and _total_ specifies the total cost of processing.
+  Optional parameter _out_ specifies the output IO.
+
+  The display of the progress bar is updated when one or
+  more percent is proceeded or one or more seconds are
+  elapsed from the previous display.
+
+- `ProgressBar#inc(step = 1)`
+
+  Increase the internal counter by _step_ and update
+  the display of the progress bar. Display the estimated
+  remaining time on the right side of the bar. The counter
+  does not go beyond the _total_.
+
+- `ProgressBar#set(count)`
+
+  Set the internal counter to _count_ and update the
+  display of the progress bar. Display the estimated
+  remaining time on the right side of the bar.  Raise if
+  _count_ is a negative number or a number more than
+  the _total_.
+
+- `ProgressBar#finish`
+
+  Stop the progress bar and update the display of progress
+  bar. Display the elapsed time on the right side of the bar.
+  The progress bar always stops at 100% by the method.
+
+- `ProgressBar#halt`
+
+  Stop the progress bar and update the display of progress
+  bar. Display the elapsed time on the right side of the bar.
+  The progress bar stops at the current percentage by the method.
+
+- `ProgressBar#format=`
+
+  Set the format for displaying a progress bar.
+  Default: `"%-14s %3d%% %s %s"`.
+
+- `ProgressBar#format_arguments=`
+
+  Set the methods for displaying a progress bar.
+  Default: `[:title, :percentage, :bar, :stat]`.
+
+- `ProgressBar#file_transfer_mode`
+
+  Use `:stat_for_file_transfer` instead of `:stat` to display
+  transfered bytes and transfer rate.
+
+
+ReverseProgressBar class is also available.  The
+functionality is identical to ProgressBar but the direction
+of the progress bar is just opposite.
+
+## Limitations
+
+Since the progress is calculated by the proportion to the
+total cost of processing, Ruby/ProgressBar cannot be used if
+the total cost of processing is unknown in advance.
+Moreover, the estimation of remaining time cannot be
+accurately performed if the progress does not flow uniformly.
+
+---
+
+[Satoru Takabayashi](http://namazu.org/~satoru/)