Update README.md

Found an issue when trying to use the library on 32-bit Node JS on a 64 bit Windows environment. Explained how to solve it in the readme.md file.
fix compile error in debug mode with assertion enabled
fix example1.js module path

I have problem to execute the example1.js.

[~/src/node-sapnwrfc] ➔ LD_LIBRARY_PATH=nwrfcsdk/lib/ node examples/example1.js

module.js:340
    throw err;
          ^
Error: Cannot find module 'sapnwrfc'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Module.require (module.js:364:17)
    at require (module.js:380:17)
    at Object.<anonymous> (/home/agebert/src/node-sapnwrfc/examples/example1.js:4:16)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
add MetaData() which returns JSON Schema for RFC functions

If you call MetaData() on a RFC function you will get parameter
as JSON Schema http://json-schema.org/ formatted.

{
  "title": "Signature of SAP RFC function Z_TEST_NESTED_TABLES",
  "type": "object",
  "properties": {
    "EP_SIMPLE": {
      "type": "integer",
      "length": "4",
      "sapType": "RFCTYPE_INT",
      "description": "Natural number",
      "sapDirection": "RFC_EXPORT"
    },
    "IP_NESTED_ARRAY": {
      "type": "array",
      "length": "1224",
      "sapType": "RFCTYPE_TABLE",
      "description": "Array of ZTEST_ARRAY",
      "sapDirection": "RFC_IMPORT",
      "items": {
        "sapTypeName": "ZTEST_TABLE_NESTED_ARRAY",
        "type": "object",
        "properties": {
          "MYTYPES": {
            "type": "object",
            "length": "1208",
            "sapType": "RFCTYPE_STRUCTURE",
            "sapTypeName": "ZTEST_TYPES",
            "properties": {
              "INTEGER_ATTRIBUTE": {
                "type": "integer",
                "length": "4",
                "sapType": "RFCTYPE_INT"
              },
              "DECIMAL_ATTRIBUTE": {
                "type": "string",
                "length": "6",
                "sapType": "RFCTYPE_BCD"
              },
              "FLOAT_ATTRIBUTE": {
                "type": "number",
                "length": "8",
                "sapType": "RFCTYPE_FLOAT"
              },
              "CHARACTER_ATTRIBUTE": {
                "type": "string",
                "length": "20",
                "sapType": "RFCTYPE_CHAR"
              },
              "DATE_ATTRIBUTE": {
                "type": "string",
                "length": "8",
                "sapType": "RFCTYPE_DATE"
              },
              "TIME_ATTRIBUTE": {
                "type": "string",
                "length": "6",
                "sapType": "RFCTYPE_TIME"
              },
              "RAW_ATTRIBUTE": {
                "type": "string",
                "length": "128",
                "sapType": "RFCTYPE_BYTE"
              },
              "SMALL_DECIMAL_ATTRIBUTE": {
                "type": "string",
                "length": "2",
                "sapType": "RFCTYPE_BCD"
              },
              "NUMC_ATTRIBUTE": {
                "type": "string",
                "length": "16",
                "sapType": "RFCTYPE_NUM"
              },
              "LCHR_ATTRIBUTE": {
                "type": "string",
                "length": "1000",
                "sapType": "RFCTYPE_CHAR"
              }
            }
          },
          "MYINTEGER": {
            "type": "integer",
            "length": "4",
            "sapType": "RFCTYPE_INT"
          },
          "MYARRAY": {
            "type": "array",
            "length": "8",
            "sapType": "RFCTYPE_TABLE",
            "items": {
              "sapTypeName": "ZTEST_TABLE_TYPES",
              "type": "object",
              "properties": {
                "INTEGER_ATTRIBUTE": {
                  "type": "integer",
                  "length": "4",
                  "sapType": "RFCTYPE_INT"
                }
              }
            }
          }
        }
      }
    }
  }
}
refactor: rename build variable msvs_nwrfcsdk_path to nwrfcsdk_path

The motivation is to use the variable for the other platforms too.
Linux build: search SAP SDK in sub-folder nwrfcsdk

I prefer to not install the SAP SDK into the system path.

You must install the SAP SDK into a sub-folder nwrfcsdk like on
Windows or you specify SAP SDK location to node-gyp.

node-gyp rebuild --nwrfcsdk_path=<YOUR PATH TO SAP SDK>

You still must install the SAP shared object files (*.so) into
system path. Or you must modify the /etc/ld.so.conf or use
LD_LIBRARY_PATH.

For example to run the example1.js:

LD_LIBRARY_PATH=nwrfcsdk/lib/ node examples/example1.js
Merge pull request #5 from LeandroDG/patch-1

Update README.md
Merge pull request #6 from e2ebridge/bug/debug_build_assert

fix compile error in debug mode with assertion enabled
Merge branch 'feature/meta_data'
Merge branch 'change/linux_build'
Added CMake build file