Document acc language features.

Original text from http://www.ioccc.org/2001/bellard.hint

libacc/FEATURES

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+
+Supported C language subset (read joint example 'otccex.c' to have
+    an introduction to OTCC dialect):
+
+    - Expressions:
+
+        * binary operators, by decreasing priority order: '*' '/' '%',
+          '+' '-', '>>' '<<', '<' '<=' '>' '>=', '==' '!=', '&',
+          '^', '|', '=', '&&', '||'.
+
+        * '&&' and '||' have the same semantics as C : left to right
+          evaluation and early exit.
+
+        * Parenthesis are supported.
+
+        * Unary operators: '&', '*' (pointer indirection), '-'
+          (negation), '+', '!', '~', post fixed '++' and '--'.
+
+        * Pointer indirection ('*') only works with explicit cast to
+          'char *', 'int *' or 'int (*)()' (function pointer).
+
+        * '++', '--', and unary '&' can only be used with variable
+          lvalue (left value).
+
+        * '=' can only be used with variable or '*' (pointer
+          indirection) lvalue.
+
+        * Function calls are supported with standard i386 calling
+          convention. Function pointers are supported with explicit
+          cast. Functions can be used before being declared.
+
+    - Types: only signed integer ('int') variables and functions can
+      be declared. Variables cannot be initialized in
+      declarations. Only old K&R function declarations are parsed
+      (implicit integer return value and no types on arguments).
+
+    - Any function or variable from the libc can be used because OTCC
+      uses the libc dynamic linker to resolve undefined symbols.
+
+    - Instructions: blocks ('{' '}') are supported as in C. 'if' and
+      'else' can be used for tests. The 'while' and 'for' C constructs
+      are supported for loops. 'break' can be used to exit
+      loops. 'return' is used for the return value of a function.
+
+    - Identifiers are parsed the same way as C. Local variables are
+      handled, but there is no local name space (not a problem if
+      different names are used for local and global variables).
+
+    - Numbers can be entered in decimal, hexadecimal ('0x' or '0X'
+      prefix), or octal ('0' prefix).
+
+    - '#define' is supported without function like arguments. No macro
+      recursion is tolerated. Other preprocessor directives are
+      ignored.
+
+    - C Strings and C character constants are supported. Only '\n',
+      '\"', '\'' and '\\' escapes are recognized.
+
+    - C Comments can be used (but no C++ comments).
+
+    - No error is displayed if an incorrect program is given.
+
+    - Memory: the code, data, and symbol sizes are limited to 100KB
+      (it can be changed in the source code).
+