add bitcoin donation button

Makefile.am

@@ -33,6 +33,7 @@ DOCS_IMAGES = \
   docs/disk_cache.png             \
   docs/utp_stack.diagram          \
   docs/utp_stack.png              \
+  docs/bitcoin.png                \
   docs/style.css                  \
   docs/rst.css                    \
   docs/img/bg.png                 \

docs/building.rst

@@ -286,6 +286,7 @@ Build features:
 | ``openssl-version``      | This can be used on windows to link against the    |
 |                          | special OpenSSL library names used on windows      |
 |                          | prior to OpenSSL 1.1.                              |
+|                          |                                                    |
 |                          | * ``1.1`` - link against the normal openssl        |
 |                          |   library name. (default)                          |
 |                          | * ``pre1.1`` - link against the old windows names  |

docs/index.rst

@@ -124,6 +124,12 @@ See the contribute_ page for other ways to help out.
 
 .. raw:: html
 
+	<span style="display:block;text-align:center;">
+	<img src="bitcoin.png" style="display:inline"><br/>
+	<a href="bitcoin:373ZDeQgQSQNuxdinNAPnQ63CRNn4iEXzg">bitcoin:373ZDeQgQSQNuxdinNAPnQ63CRNn4iEXzg</a>
+	</span>
+	
+	<span style="display:block;text-align:center;margin-top:1em">
 	<span style="display:inline-block">
 	<a class="FlattrButton" style="display:none;" href="http://libtorrent.org"></a>
 	<noscript><a href="https://flattr.com/thing/95662/libtorrent" target="_blank">
@@ -142,6 +148,7 @@ See the contribute_ page for other ways to help out.
 	<img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
 	</form>
 	</span>
+	</span>
 
 
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