Improve writeup.

doc/src/language/other-op.md

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+Other Operators
+===============
+
+{{#include ../links.md}}
+
+
+Compound Assignment Operators
+----------------------------
+
+```rust
+let number = 9;
+
+number += 8;            // number = number + 8
+
+number -= 7;            // number = number - 7
+
+number *= 6;            // number = number * 6
+
+number /= 5;            // number = number / 5
+
+number %= 4;            // number = number % 4
+
+number ~= 3;            // number = number ~ 3
+
+number <<= 2;           // number = number << 2
+
+number >>= 1;           // number = number >> 1
+
+number &= 0x00ff;       // number = number & 0x00ff;
+
+number |= 0x00ff;       // number = number | 0x00ff;
+
+number ^= 0x00ff;       // number = number ^ 0x00ff;
+```
+
+
+The Flexible `+=`
+----------------
+
+The `+=` operator can also be used to build [strings]:
+
+```rust
+let my_str = "abc";
+my_str += "ABC";
+my_str += 12345;
+
+my_str == "abcABC12345"
+```
+
+It may also be used to concatenate [arrays]:
+
+```rust
+let my_array = [1, 2, 3];
+my_array += [4, 5];
+
+my_array == [1, 2, 3, 4, 5];
+```
+
+or mix two [object maps] together:
+
+```rust
+let my_obj = #{a:1, b:2};
+my_obj += #{c:3, d:4, e:5};
+
+my_obj.len() == 5;
+```