[Ethereum] ParserError: Expected identifier, got ‘LParen’ constructor() public {

There is several problems with your code.

You copy paste the function prototype instead of calling it you should use im_myAddressUintMap.insert( key, value);

And you have to make this insert inside a function or inside the constructor ( function with the name of the contract )

function insert( address key, uint value ) public {
    im_myAddressUintMap.insert( key, value );
}

so the contract should be something like this

second import is to test on remix

pragma solidity ^0.4.15;

import "./itMapsLib.sol";  
//import "https://github.com/szerintedmi/solidity-itMapsLib/itMapsLib.sol";    

contract User
{
  using itMaps for itMaps.itMapAddressUint;

  itMaps.itMapAddressUint im_myAddressUintMap;

  function insert ( address key, uint value) public {
    im_myAddressUintMap.insert( key, value);
  }
}

Edit : you edited your contract. The last error you have is the incorrect import of using itMaps for itMaps.itMapUintAddress; you're using itMapAddressUint

I had a similar problem. In my case, it was the system version of solc I had installed. Here's what I had. I had solc installed through Homebrew, and also truffle installed. When I run truffle version:

Truffle v4.1.14 (core: 4.1.14)
Solidity v0.4.24 (solc-js)

So I had the latest version of truffle and, seemingly, solc as well. However, when I run solc --version:

solc, the solidity compiler commandline interface
Version: 0.4.19+commit.e67f0147.Darwin.appleclang

My system solidity version was different. I found that I had installed solidity through Homebrew (on Mac), so that was different from the version truffle was using. So the fix, in my case, was to upgrade solidity using homebrew. It upgraded from 0.4.19 to 0.4.24 and my problem went away. To upgrade solidity using Homebrew:

brew update
brew upgrade
brew tap ethereum/ethereum
brew install solidity
brew linkapps solidity

The first two lines are probably all you need if you already have solidity installed, but I added the rest for completeness.

While this was on Mac, the same issue might exist on Linux. Make sure you update the system installed version of solc, not just what's installed with truffle.