FEATURE: server side support for upload:// markdown

This allows uploads to be specified using short sha1 hash instead of full
URL

Client side change is pending

lib/base62.rb

@@ -0,0 +1,35 @@
+# Modified version of: https://github.com/steventen/base62-rb
+
+module Base62
+  KEYS = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".freeze
+  KEYS_HASH = KEYS.each_char.with_index.inject({}) { |h, (k, v)| h[k] = v; h }
+  BASE = KEYS.length
+
+  # Encodes base10 (decimal) number to base62 string.
+  def self.encode(num)
+    return "0" if num == 0
+    return nil if num < 0
+
+    str = ""
+    while num > 0
+      # prepend base62 charaters
+      str = KEYS[num % BASE] + str
+      num = num / BASE
+    end
+    str
+  end
+
+  # Decodes base62 string to a base10 (decimal) number.
+  def self.decode(str)
+    num = 0
+    i = 0
+    len = str.length - 1
+    # while loop is faster than each_char or other 'idiomatic' way
+    while i < str.length
+      pow = BASE**(len - i)
+      num += KEYS_HASH[str[i]] * pow
+      i += 1
+    end
+    num
+  end
+end