Install H3 via native extension if it isn't present.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "ext/h3/src"]
+	path = ext/h3/src
+	url = https://github.com/uber/h3.git

.travis.yml

@@ -1,6 +1,5 @@
 install:
-  - git clone https://github.com/uber/h3.git h3_build
-  - pushd h3_build
+  - pushd ext/h3/src
   - cmake . -DBUILD_SHARED_LIBS=true
   - make
   - sudo make install

README.md

@@ -24,19 +24,9 @@ We have also suffixed predicate methods with a question mark, as per the Ruby co
 
 This gem uses FFI to link directly into the H3 library (written in C).
 
-Before using the gem, you will need to install the C lib at https://github.com/uber/h3.
+The gem is installed as a native extension. It requires some dependencies to be present on the system first.
 
-Install the build dependencies as instructed here: https://github.com/uber/h3#install-build-time-dependencies
-
-Do *not* follow the Compilation Steps. Instead, use the following:
-
-    git clone [email protected]:uber/h3.git h3_build
-    cd h3_build
-    cmake . -DBUILD_SHARED_LIBS=true
-    make
-    sudo make install
-
-The key difference is the `BUILD_SHARED_LIBS` option.
+Please install the build dependencies for your system as instructed here: https://github.com/uber/h3#install-build-time-dependencies
 
 ## Installing
 

ext/h3/extconf.rb

@@ -0,0 +1,19 @@
+require "mkmf"
+
+make_content = "make:\n" \
+               "\tcd src;" \
+               "\tcmake . -DBUILD_SHARED_LIBS=true;" \
+               "\tmake\n" \
+               "install:\n" \
+               "\tcd src; make install ; true\n" \
+               "clean:\n" \
+               "\t:\n"
+
+dummy_content = "make:\n" \
+               "\t:\n" \
+               "install:\n" \
+               "\t:\n" \
+               "clean:\n" \
+               "\t:\n"
+
+File.write('Makefile', have_library("h3") ? dummy_content : make_content)

h3.gemspec

@@ -10,7 +10,7 @@ Gem::Specification.new do |spec|
   spec.email    = "[email protected]"
 
   spec.required_ruby_version = "> 2.3"
-  spec.files = `git ls-files`.split("\n")
+  spec.files = `git ls-files --recurse-submodules`.split("\n")
 
   spec.add_runtime_dependency "ffi", "~> 1.9"
   spec.add_runtime_dependency "rgeo-geojson", "~> 2.1"
@@ -19,4 +19,6 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rspec", "~> 3.8"
   spec.add_development_dependency "yard", "~> 0.9"
   spec.add_development_dependency "coveralls", "~> 0.8"
+
+  spec.extensions << 'ext/h3/extconf.rb'
 end