Add licence and readme files

LICENCE

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+Copyright (c) 2010 Olivier Poitrey <rs@dailymotion.com>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is furnished
+to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

README.md

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+On iPhone OS, Apple did remove on-disk cache support for unknown reason. Some will say it's to save
+flash-drive life, others will arg it's to save disk capacity. As it is explained in the
+NSURLCacheStoragePolicy, the NSURLCacheStorageAllowed constant is always treated as
+NSURLCacheStorageAllowedInMemoryOnly and there is no way to force it back, the code is certainly
+gone on this platform. For whatever reason Apple removed this feature, you may be interested by
+having on-disk HTTP request caching in your application. SDURLCache gives back this feature to this
+iPhone OS for you.
+
+To use it, you just have create an instance, replace the default shared NSURLCache with it and
+that's it, you instantly give on-disk HTTP request caching capability to your application.
+
+    SDURLCache *urlCache = [[SDURLCache alloc] initWithMemoryCapacity:1024*1024   // 1MB mem cache
+                                                         diskCapacity:1024*1024*5 // 5MB disk cache
+                                                             diskPath:[SDURLCache defaultCachePath]];
+    [NSURLCache setSharedURLCache:urlCache];
+    [urlCache release];
+
+To save flash drive, SDURLCache doesn't cache on disk responses which cache max-age is lower than
+5 minutes by default. You can change this behavior by changing the `minCacheInterval` property.
+
+Cache eviction is done automatically on cache-in, when disk capacity is outreached. All write disk
+operation like cache storing or evicting is done in a separated thread (using NSOperation) so it
+won't block the NSURLConnection run loop thread.
+
+To control the caching behavior, use the `NSURLRequest`'s `cachePolicy` property. If you want a
+response not to be cached on disk but still in memory, you can implement the `NSURLConnection`
+`connection:willCacheResponse:` delegate method and change the `NSURLCachedResponse` `storagePolicy`
+property to `NSURLCacheStorageAllowedInMemoryOnly`. See example below:
+
+    - (NSCachedURLResponse *)connection:(NSURLConnection *)connection
+                      willCacheResponse:(NSCachedURLResponse *)cachedResponse
+    {
+        NSCachedURLResponse *memOnlyCachedResponse =
+            [[NSCachedURLResponse alloc] initWithResponse:cachedResponse.response
+                                                     data:cachedResponse.data
+                                                 userInfo:cachedResponse.userInfo
+                                            storagePolicy:NSURLCacheStorageAllowedInMemoryOnly];
+        return [memOnlyCachedResponse autorelease];
+    }