Local project checks and contribution templates: make check, dependency-free C/python tests, issue forms + blank issues, CONTRIBUTING (#20)

* Add lightweight project checks and templates

* Ignore generated test binaries

* Keep project checks local

c/tests/test_json.c

@@ -0,0 +1,36 @@
+#include <math.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "../json.h"
+
+#define CHECK(condition) do { \
+    if (!(condition)) { \
+        fprintf(stderr, "%s:%d: check failed: %s\n", __FILE__, __LINE__, #condition); \
+        return 1; \
+    } \
+} while (0)
+
+int main(void) {
+    jval *root = json_parse(
+        "{\"name\":\"Colibri\\nCPU\",\"enabled\":true,\"empty\":null,"
+        "\"values\":[1,-2.5,3e2],\"unicode\":\"\\u03bb \\uD83D\\uDE80\"}",
+        NULL
+    );
+
+    CHECK(root && root->t == J_OBJ);
+    CHECK(strcmp(json_get(root, "name")->str, "Colibri\nCPU") == 0);
+    CHECK(json_get(root, "enabled")->boolean == 1);
+    CHECK(json_get(root, "empty")->t == J_NULL);
+    CHECK(json_get(root, "missing") == NULL);
+
+    jval *values = json_get(root, "values");
+    CHECK(values->t == J_ARR && values->len == 3);
+    CHECK(values->kids[0]->num == 1.0);
+    CHECK(values->kids[1]->num == -2.5);
+    CHECK(values->kids[2]->num == 300.0);
+    CHECK(strcmp(json_get(root, "unicode")->str, "λ 🚀") == 0);
+
+    puts("json tests: ok");
+    return 0;
+}