Added usage samples (SharePoint#573)

* Added usage sample

* Added sample

* Added validate sample

Author: KoenZomers

reference/spfx/sp-core-library/log.md

@@ -22,7 +22,16 @@ The Log class provides static methods for logging messages at different levels (
 |[`verbose(source,message,scope)`](verbose-log.md)     | `public, static` | `void` | Logs a verbose message |
 |[`warn(source,message,scope)`](warn-log.md)     | `public, static` | `void` | Logs a warning |
 
-
-
-
-
+## Sample
+```ts
+import {
+  Log
+} from '@microsoft/sp-core-library';
+
+// ...
+Log.error("sample", new Error("error message"));
+Log.info("sample", "informational message");
+Log.warn("sample", "warning message");
+Log.verbose("sample", "verbose message");
+// ...
+```

reference/spfx/sp-core-library/urlqueryparametercollection.md

@@ -32,7 +32,18 @@ None
 |[`getValue(param)`](getvalue-urlqueryparametercollection.md)     | `public` | `string` | Returns the value of the first matching query parameter or undefined if the key doesn't exist. Examples: this._queryParameterList = [ {key: TEST, value: done}, {key: DEBUG, value: false}, {key: TEST, value: notdone}] getValue('TEST') ---> 'done' getValue('debug') ---> 'false' getValue('lost') ---> undefined |
 |[`getValues(param)`](getvalues-urlqueryparametercollection.md)     | `public` | `string[]` | Returns the values of all of the matching query parameters or undefined if the key doesn't exist. Examples: this._queryParameterList = [ {key: TEST, value: done}, {key: DEBUG, value: false}, {key: TEST, value: notdone}] getValues('TEST') ---> ['done', 'notdone'] getValues('debug') ---> ['false'] getValues('lost') ---> undefined |
 
-
+## Sample
+
+```ts
+import {
+  UrlQueryParameterCollection
+} from '@microsoft/sp-core-library';
+
+// ...
+let queryParameterCollection = new UrlQueryParameterCollection(document.URL);
+let idValue = queryParameterCollection.getValue("id");
+// ...
+```
 
 
 

reference/spfx/sp-core-library/validate.md

@@ -21,7 +21,13 @@ This class implements provides a standard way to validate properties and functio
 |[`isNotNullOrUndefined(value,variableName)`](isnotnullorundefined-validate.md)     | `public, static` | `void` | Throws an exception if the specified value is null or undefined. |
 |[`isTrue(value,variableName)`](istrue-validate.md)     | `public, static` | `void` | Throws an exception if the specified value is not true. |
 
-
-
-
-
+## Sample
+```ts
+import {
+  Validate
+} from '@microsoft/sp-core-library';
+
+Validate.isNonemptyString(idValue, "idValue");
+Validate.isNotNullOrUndefined(idValue, "idValue");
+Validate.isTrue((idValue !== undefined), "idValue");
+```