feat: new page for functions

[novusnota]

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WIP: WIP

Closes #131

[anton-trunov]

Any progress here?

[anton-trunov]

Any progress here?

[anton-trunov]

we need this page asap, especially with enhanced section on native functions showing how to FFI with FunC

[anton-trunov]

for instance, here is an example of a binding for FunC's parse_std_addr function:

;; FunC
(int, int) parse_std_addr(slice s) asm "REWRITESTDADDR";

// Tact
struct Addr {
    workchain: Int;
    address: Int;
}

@name(parse_std_addr)
native parseStdAddr(s: Slice): Addr;

(caveat emptor: I haven't tested it)

[anton-trunov]

Any progress here?

[novusnota]

Closed in favor of opening a new PR in https://github.com/tact-lang/tact

The commits here should be kept for a while, so the branch must not be deleted!